From e0f5e14bdb83c232272d4d685d2c06734611145e Mon Sep 17 00:00:00 2001
From: "Paolo G. Giarrusso" <paolo@skylabs-ai.com>
Date: Wed, 11 Feb 2026 17:09:54 +0100
Subject: [PATCH 01/11] More examples, with a loop invariant

---
 rocq-brick-libstdcpp/test/dune.inc            | 18 +++++++++
 .../test/geeks_for_geeks_examples/N3_sum.cpp  | 11 ++++++
 .../test/geeks_for_geeks_examples/N3_sum.v    | 20 ++++++++++
 .../geeks_for_geeks_examples/N3_sum_a.cpp     | 18 +++++++++
 .../test/geeks_for_geeks_examples/N3_sum_a.v  | 37 +++++++++++++++++++
 5 files changed, 104 insertions(+)
 create mode 100644 rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum.cpp
 create mode 100644 rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum.v
 create mode 100644 rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum_a.cpp
 create mode 100644 rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum_a.v

diff --git a/rocq-brick-libstdcpp/test/dune.inc b/rocq-brick-libstdcpp/test/dune.inc
index a5b255d..e1d3ecf 100644
--- a/rocq-brick-libstdcpp/test/dune.inc
+++ b/rocq-brick-libstdcpp/test/dune.inc
@@ -35,6 +35,24 @@
                          (run cpp2v -v %{input} -o N2_input_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
  (alias (name srcs) (deps N2_input.cpp))
 )
+(subdir geeks_for_geeks_examples
+ (rule
+  (targets N3_sum_cpp.v)
+  (alias test_ast)
+  (deps (:input N3_sum.cpp) (glob_files_rec ../*.hpp) (universe))
+  (action
+                         (run cpp2v -v %{input} -o N3_sum_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
+ (alias (name srcs) (deps N3_sum.cpp))
+)
+(subdir geeks_for_geeks_examples
+ (rule
+  (targets N3_sum_a_cpp.v)
+  (alias test_ast)
+  (deps (:input N3_sum_a.cpp) (glob_files_rec ../*.hpp) (universe))
+  (action
+                         (run cpp2v -v %{input} -o N3_sum_a_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
+ (alias (name srcs) (deps N3_sum_a.cpp))
+)
 (subdir geeks_for_geeks_examples
  (rule
   (targets iostream_cpp.v)
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum.cpp b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum.cpp
new file mode 100644
index 0000000..f0bf9b0
--- /dev/null
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum.cpp
@@ -0,0 +1,11 @@
+#include <iostream>
+using namespace std;
+
+int main() {
+    int a = 11, b = 9;
+
+    // Adding the two numbers and printing
+    // their sum
+    cout << a + b;
+    return 0;
+}
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum.v
new file mode 100644
index 0000000..e62a246
--- /dev/null
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum.v
@@ -0,0 +1,20 @@
+Require Import skylabs.auto.cpp.prelude.proof.
+Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.spec.
+
+Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.N3_sum_cpp.
+
+Import linearity.
+
+Section with_cpp.
+  Context `{Σ : cpp_logic, σ : genv}.
+
+  cpp.spec "main()" from source as main_spec with (
+    \prepost{osM} _global "std::cout" |-> ostreamR 1$m osM
+    \pre{str} _global "std::cout" |-> ostream_contentR 1$m str
+    \post[Vint 0]
+      _global "std::cout" |-> ostream_contentR 1$m (str ++ Z_to_string 20)
+  ).
+
+  Lemma main_ok : verify?[source] main_spec.
+  Proof. verify_spec; go. Qed.
+End with_cpp.
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum_a.cpp b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum_a.cpp
new file mode 100644
index 0000000..9323d4c
--- /dev/null
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum_a.cpp
@@ -0,0 +1,18 @@
+#include <iostream>
+using namespace std;
+
+int main() {
+    int a = 11, b = 9;
+
+    // If b is positive, increment a to b times
+    for (int i = 0; i < b; i++)
+        a++;
+
+    // If b is negative, decrement a to |b| times
+    for (int i = 0; i > b; i--)
+        a--;
+
+    cout << a;
+
+    return 0;
+}
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum_a.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum_a.v
new file mode 100644
index 0000000..d6047de
--- /dev/null
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum_a.v
@@ -0,0 +1,37 @@
+Require Import skylabs.auto.cpp.prelude.proof.
+Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.spec.
+
+Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.N3_sum_a_cpp.
+
+Import linearity.
+
+Section with_cpp.
+  Context `{Σ : cpp_logic, σ : genv}.
+
+  cpp.spec "main()" from source as main_spec with (
+    \prepost{osM} _global "std::cout" |-> ostreamR 1$m osM
+    \pre{str} _global "std::cout" |-> ostream_contentR 1$m str
+    \post[Vint 0]
+      _global "std::cout" |-> ostream_contentR 1$m (str ++ Z_to_string 20)
+  ).
+
+  #[global] Declare Instance Z_to_string_inj : Inj eq eq Z_to_string.
+
+  Lemma main_ok : verify?[source] main_spec.
+  Proof.
+    verify_spec; go.
+
+    wp_for (fun ρ =>
+      \pre{i1} _local ρ "i" |-> intR 1$m i1
+      \pre _local ρ "a" |-> intR 1$m (11 + i1)
+      \require 0 <= i1 <= 9
+      \post* _local ρ "i" |-> anyR "int" 1$m
+      \post* _local ρ "a" |-> intR 1$m 20
+      \post emp
+    ).
+
+    go.
+    wp_if; go.
+    wp_for (fun ρ => emp); go.
+  Qed.
+End with_cpp.

From 9fc58884be567e99722139cd9e9053f356de6211 Mon Sep 17 00:00:00 2001
From: "Paolo G. Giarrusso" <paolo@skylabs-ai.com>
Date: Wed, 11 Feb 2026 19:14:14 +0100
Subject: [PATCH 02/11] Example 5

---
 rocq-brick-libstdcpp/test/dune.inc            |   9 ++
 .../test/geeks_for_geeks_examples/N5_swap.cpp |  17 ++
 .../test/geeks_for_geeks_examples/N5_swap.v   | 146 ++++++++++++++++++
 .../test/geeks_for_geeks_examples/spec.v      |   5 +
 4 files changed, 177 insertions(+)
 create mode 100644 rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.cpp
 create mode 100644 rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v

diff --git a/rocq-brick-libstdcpp/test/dune.inc b/rocq-brick-libstdcpp/test/dune.inc
index e1d3ecf..ffc3af3 100644
--- a/rocq-brick-libstdcpp/test/dune.inc
+++ b/rocq-brick-libstdcpp/test/dune.inc
@@ -53,6 +53,15 @@
                          (run cpp2v -v %{input} -o N3_sum_a_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
  (alias (name srcs) (deps N3_sum_a.cpp))
 )
+(subdir geeks_for_geeks_examples
+ (rule
+  (targets N5_swap_cpp.v)
+  (alias test_ast)
+  (deps (:input N5_swap.cpp) (glob_files_rec ../*.hpp) (universe))
+  (action
+                         (run cpp2v -v %{input} -o N5_swap_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
+ (alias (name srcs) (deps N5_swap.cpp))
+)
 (subdir geeks_for_geeks_examples
  (rule
   (targets iostream_cpp.v)
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.cpp b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.cpp
new file mode 100644
index 0000000..e1e67d6
--- /dev/null
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.cpp
@@ -0,0 +1,17 @@
+// https://www.geeksforgeeks.org/cpp/cpp-program-to-swap-two-numbers/
+#include <iostream>
+using namespace std;
+
+int main(){
+    int a = 2, b = 3;
+
+    cout << "Before swapping a = " << a << " , b = " << b << endl;
+
+    int temp;
+
+    temp = a;
+    a = b;
+    b = temp;
+    cout << "After swapping a = " << a << " , b = " << b << endl;
+    return 0;
+}
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v
new file mode 100644
index 0000000..80c653f
--- /dev/null
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v
@@ -0,0 +1,146 @@
+Require Import skylabs.auto.cpp.prelude.proof.
+Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.spec.
+
+Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.N5_swap_cpp.
+
+Import linearity.
+
+Section with_cpp.
+  Context `{Σ : cpp_logic, σ : genv}.
+
+  cpp.spec "main()" from source as main_spec with (
+    \prepost{osM} _global "std::cout" |-> ostreamR 1$m osM
+    \pre{str} _global "std::cout" |-> ostream_contentR 1$m str
+    \post[Vint 0]
+      _global "std::cout" |-> ostream_contentR 1$m
+        (str ++
+        "Before swapping a = " ++
+        Z_to_string 2 ++ " , b = " ++ Z_to_string 3 ++ "\n" ++
+        "After swapping a = " ++ Z_to_string 3 ++ " , b = " ++ Z_to_string 2 ++ "\n"
+      )
+  ).
+
+  Definition iostream_manip_spec f : WpSpec_cpp_val := (
+    \arg{osP : ptr} "" (Vptr osP)
+    \prepost{osM} osP |-> ostreamR 1$m osM
+    \pre{str} osP |-> ostream_contentR 1$m str
+    \post[Vptr osP] osP |-> ostream_contentR 1$m (f str)).
+
+  Definition ostream_cpp_type : type :=
+    "std::basic_ostream<char, std::char_traits<char>>&".
+  Definition iostream_manip_kind : okind :=
+    tFunction ostream_cpp_type [ostream_cpp_type].
+
+  cpp.spec "std::endl<char, std::char_traits<char>>(std::basic_ostream<char, std::char_traits<char>>&)" from source as endl_spec with (
+    \exact Reduce iostream_manip_spec (fun str => str ++ "\n")%bs
+  ).
+
+  (* This is the overload taking the endl manipulator. *)
+  cpp.spec "std::basic_ostream<char, std::char_traits<char>>::operator<<(std::basic_ostream<char, std::char_traits<char>>&(*)(std::basic_ostream<char, std::char_traits<char>>&))" from source as ostream_insert_string_spec with (
+    \this this
+    \arg{os_f} "" (Vptr os_f)
+    \pre{stream_f}
+      os_f |-> unmaterialized_specR
+        iostream_manip_kind
+        (iostream_manip_spec stream_f)
+    \prepost{osM} this |-> ostreamR 1$m osM
+    \pre{str} this |-> ostream_contentR 1$m str
+    \post[Vptr this]
+      this |-> ostream_contentR 1$m (stream_f str)
+  ).
+
+  #[program]
+  Definition hint_stream_F :=
+    \cancelx@{mpredI}
+    \bound_existential (stream_f : cstring.t → cstring.t)
+    \instantiate stream_f := fun str => (str ++ "\n")%bs
+    \end.
+  Next Obligation. work. Qed.
+
+  (* #[program]
+  Definition hint_stream_F :=
+    \cancelx@{mpredI}
+    \bound_existential (stream_f : cstring.t → cstring.t)
+    (* \goal_trigger{os_f : ptr}
+      os_f |-> unmaterialized_specR
+        iostream_manip_kind
+        (iostream_manip_spec stream_f) *)
+    \goal_trigger{os_f : ptr}
+      os_f |-> cptrR
+        iostream_manip_kind
+        (iostream_manip_spec stream_f)
+    \instantiate stream_f := (fun str => str ++ "\n")%bs
+
+    \end.
+  Next Obligation. work. Qed. *)
+
+  Lemma main_ok : verify?[source] main_spec.
+  Proof.
+    verify_shift; go.
+
+(**
+_ : denoteModule source
+_ : ostream_insert_string_spec
+_ : endl_spec
+_ : ostream_print_int_spec
+_ : ostream_insert_spec
+_ : type_ptr "int" a_addr
+_ : type_ptr "int" b_addr
+_ : type_ptr "char" _x_1
+_ : ∀ q : Qp, _x_1 |-> cstring.R q$c "Before swapping a = " ={⊤}=∗ emp
+_ : type_ptr "char" _x_4
+_ : ∀ q : Qp, _x_4 |-> cstring.R q$c " , b = " ={⊤}=∗ emp
+--------------------------------------□
+_ : PostCond
+_ : _x_1 |-> cstring.R _x_2$c "Before swapping a = "
+_ : a_addr |-> intR 1$m 2
+_ : _x_4 |-> cstring.R _x_5$c " , b = "
+_ : b_addr |-> intR 1$m 3
+--------------------------------------∗
+∃ stream_f : cstring.t → cstring.t,
+_global "std::endl<char, std::char_traits<char>>(std::basic_ostream<char, std::char_traits<char>>&)"
+|-> cptrR
+(unmaterialized_fspec (tFunction ostream_cpp_type [ostream_cpp_type])
+(add_with
+(λ osP : ptr,
+add_arg (Vptr osP)
+(add_with
+(λ osM0 : ostreamT,
+add_pre ([...])
+([...])) "osM" DummyValue)) "osP" DummyValue)) ∗
+(_global "std::cout" |-> ostreamR 1$m osM ∗
+_global "std::cout"
+|-> ostream_contentR 1$m
+(stream_f ((((str ++ "Before swapping a = ") ++ Z_to_string 2) ++ " , b = ") ++ Z_to_string 3)%bs) -∗
+interp source 1
+(interp source ((1 >*> 1) >*> ((1 >*> 1) >*> ((1 >*> 1) >*> (([...]) >*> ([...])))))
+(wp_block source [region: "b" @ b_addr; "a" @ a_addr; return {?: "int"}]
+[Sdecl [Dvar "temp" "int" None]; Sexpr (Eassign (Evar "temp" "int") (Ecast Cl2r ([...])) "int");
+Sexpr (Eassign (Evar "a" "int") (Ecast Cl2r ([...])) "int");
+Sexpr (Eassign (Evar "b" "int") (Ecast Cl2r ([...])) "int");
+Sexpr
+(Eoperator_call OOLessLess
+(operator_impl.MFunc
+"std::basic_ostream<char, std::char_traits<char>>::operator<<(std::basic_ostream<char, std::char_traits<char>>&(*)(std::basic_ostream<char, std::char_traits<char>>&))"%cpp_name
+Direct
+"std::basic_ostream<char, std::char_traits<char>>&(std::basic_ostream<char, std::char_traits<char>>&(*)(std::basic_ostream<char, std::char_traits<char>>&))"%cpp_type)
+[Eoperator_call OOLessLess
+([...])
+[[...];
+[...]];
+Ecast Cfun2ptr
+([...])]);
+Sreturn (Some (Eint 0 "int"))]
+(Kfree source ((1 >*> FreeTemps.delete "int" b_addr) >*> FreeTemps.delete "int" a_addr)
+(Kcleanup source [] (Kreturn ([...])))))))
+*)
+
+    iExists (_ : cstring.t → cstring.t); work with br_erefl; go.
+    (* iExists (fun str => str ++ "\n")%bs; go. *)
+    iExists (_ : cstring.t → cstring.t); work with br_erefl; go.
+    banish_string_literals.
+    iModIntro.
+    rewrite -!(assoc_L BS.append).
+    go.
+  Qed.
+End with_cpp.
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v
index bcc48b1..1d874c9 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v
@@ -16,6 +16,11 @@ Proof.
   elim: x => [|x xs /= IH] [|y1 ys1] [|y2 ys2] //= [/(inj (BS.append _))] //.
 Qed.
 
+#[global] Instance BS_append_assoc : Assoc eq BS.append.
+Proof.
+  elim => [|x xs IH] [|y ys] [|z zs] //=. all: by rewrite -IH.
+Qed.
+
 #[global] Instance refine_bs_app' (str a b : BS.t) :
   Refine1 true true (str ++ a = str ++ b)%bs [a = b].
 Proof. tac_refine. move: H. apply: inj. Qed.

From 4e662c25039db5228d140ea729900e6107af86c5 Mon Sep 17 00:00:00 2001
From: "Paolo G. Giarrusso" <paolo@skylabs-ai.com>
Date: Wed, 11 Feb 2026 19:53:41 +0100
Subject: [PATCH 03/11] iostream spec: Let stream manipulators modify stream
 state

---
 .../test/geeks_for_geeks_examples/N5_swap.v   | 29 +++++++++++--------
 .../test/geeks_for_geeks_examples/spec.v      |  2 ++
 2 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v
index 80c653f..f0c3e58 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v
@@ -20,11 +20,13 @@ Section with_cpp.
       )
   ).
 
-  Definition iostream_manip_spec f : WpSpec_cpp_val := (
+  Definition iostream_manip_spec state_f contents_f : WpSpec_cpp_val := (
     \arg{osP : ptr} "" (Vptr osP)
-    \prepost{osM} osP |-> ostreamR 1$m osM
+    (* XXX: manipulators can modify [osM]! *)
+    \pre{osM} osP |-> ostreamR 1$m osM
+    \post* osP |-> ostreamR 1$m (state_f osM)
     \pre{str} osP |-> ostream_contentR 1$m str
-    \post[Vptr osP] osP |-> ostream_contentR 1$m (f str)).
+    \post[Vptr osP] osP |-> ostream_contentR 1$m (contents_f str)).
 
   Definition ostream_cpp_type : type :=
     "std::basic_ostream<char, std::char_traits<char>>&".
@@ -32,18 +34,19 @@ Section with_cpp.
     tFunction ostream_cpp_type [ostream_cpp_type].
 
   cpp.spec "std::endl<char, std::char_traits<char>>(std::basic_ostream<char, std::char_traits<char>>&)" from source as endl_spec with (
-    \exact Reduce iostream_manip_spec (fun str => str ++ "\n")%bs
+    \exact Reduce iostream_manip_spec (fun osM => osM) (fun str => str ++ "\n")%bs
   ).
 
   (* This is the overload taking the endl manipulator. *)
   cpp.spec "std::basic_ostream<char, std::char_traits<char>>::operator<<(std::basic_ostream<char, std::char_traits<char>>&(*)(std::basic_ostream<char, std::char_traits<char>>&))" from source as ostream_insert_string_spec with (
     \this this
     \arg{os_f} "" (Vptr os_f)
-    \pre{stream_f}
+    \pre{state_f stream_f}
       os_f |-> unmaterialized_specR
         iostream_manip_kind
-        (iostream_manip_spec stream_f)
-    \prepost{osM} this |-> ostreamR 1$m osM
+        (iostream_manip_spec state_f stream_f)
+    \pre{osM} this |-> ostreamR 1$m osM
+    \post* this |-> ostreamR 1$m (state_f osM)
     \pre{str} this |-> ostream_contentR 1$m str
     \post[Vptr this]
       this |-> ostream_contentR 1$m (stream_f str)
@@ -53,7 +56,9 @@ Section with_cpp.
   Definition hint_stream_F :=
     \cancelx@{mpredI}
     \bound_existential (stream_f : cstring.t → cstring.t)
+    \bound_existential (state_f : ostreamT → ostreamT)
     \instantiate stream_f := fun str => (str ++ "\n")%bs
+    \instantiate state_f := fun osM => osM
     \end.
   Next Obligation. work. Qed.
 
@@ -68,7 +73,7 @@ Section with_cpp.
     \goal_trigger{os_f : ptr}
       os_f |-> cptrR
         iostream_manip_kind
-        (iostream_manip_spec stream_f)
+        (iostream_manip_spec state_f stream_f)
     \instantiate stream_f := (fun str => str ++ "\n")%bs
 
     \end.
@@ -135,12 +140,12 @@ Sreturn (Some (Eint 0 "int"))]
 (Kcleanup source [] (Kreturn ([...])))))))
 *)
 
-    iExists (_ : cstring.t → cstring.t); work with br_erefl; go.
-    (* iExists (fun str => str ++ "\n")%bs; go. *)
-    iExists (_ : cstring.t → cstring.t); work with br_erefl; go.
+    (* iExists id, (fun str => str ++ "\n")%bs; go. *)
+    iExists (_ : ostreamT → ostreamT), (_ : cstring.t → cstring.t); work with br_erefl; go.
+    iExists (_ : ostreamT → ostreamT), (_ : cstring.t → cstring.t); work with br_erefl; go.
     banish_string_literals.
     iModIntro.
     rewrite -!(assoc_L BS.append).
-    go.
+    work.
   Qed.
 End with_cpp.
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v
index 1d874c9..1dafe13 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v
@@ -25,6 +25,8 @@ Qed.
   Refine1 true true (str ++ a = str ++ b)%bs [a = b].
 Proof. tac_refine. move: H. apply: inj. Qed.
 
+#[global] Arguments BS.append : simpl never.
+
 Section with_cpp.
   Context `{Σ : cpp_logic, σ : genv}.
 

From 34a7b72c5f07d1cd5176dbb5f8b8ff1e69bf82fb Mon Sep 17 00:00:00 2001
From: "Paolo G. Giarrusso" <paolo@skylabs-ai.com>
Date: Wed, 11 Feb 2026 21:44:10 +0100
Subject: [PATCH 04/11] Upstream specs

---
 .../test/geeks_for_geeks_examples/N5_swap.v   | 32 ---------------
 .../test/geeks_for_geeks_examples/spec.v      | 41 +++++++++++++++++++
 2 files changed, 41 insertions(+), 32 deletions(-)

diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v
index f0c3e58..64b852a 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v
@@ -20,38 +20,6 @@ Section with_cpp.
       )
   ).
 
-  Definition iostream_manip_spec state_f contents_f : WpSpec_cpp_val := (
-    \arg{osP : ptr} "" (Vptr osP)
-    (* XXX: manipulators can modify [osM]! *)
-    \pre{osM} osP |-> ostreamR 1$m osM
-    \post* osP |-> ostreamR 1$m (state_f osM)
-    \pre{str} osP |-> ostream_contentR 1$m str
-    \post[Vptr osP] osP |-> ostream_contentR 1$m (contents_f str)).
-
-  Definition ostream_cpp_type : type :=
-    "std::basic_ostream<char, std::char_traits<char>>&".
-  Definition iostream_manip_kind : okind :=
-    tFunction ostream_cpp_type [ostream_cpp_type].
-
-  cpp.spec "std::endl<char, std::char_traits<char>>(std::basic_ostream<char, std::char_traits<char>>&)" from source as endl_spec with (
-    \exact Reduce iostream_manip_spec (fun osM => osM) (fun str => str ++ "\n")%bs
-  ).
-
-  (* This is the overload taking the endl manipulator. *)
-  cpp.spec "std::basic_ostream<char, std::char_traits<char>>::operator<<(std::basic_ostream<char, std::char_traits<char>>&(*)(std::basic_ostream<char, std::char_traits<char>>&))" from source as ostream_insert_string_spec with (
-    \this this
-    \arg{os_f} "" (Vptr os_f)
-    \pre{state_f stream_f}
-      os_f |-> unmaterialized_specR
-        iostream_manip_kind
-        (iostream_manip_spec state_f stream_f)
-    \pre{osM} this |-> ostreamR 1$m osM
-    \post* this |-> ostreamR 1$m (state_f osM)
-    \pre{str} this |-> ostream_contentR 1$m str
-    \post[Vptr this]
-      this |-> ostream_contentR 1$m (stream_f str)
-  ).
-
   #[program]
   Definition hint_stream_F :=
     \cancelx@{mpredI}
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v
index 1dafe13..87c0ddc 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v
@@ -63,4 +63,45 @@ Section with_cpp.
         this |-> ostream_contentR 1$m (str ++ Z_to_string n)
   ).
 
+  cpp.spec "std::basic_ostream<char, std::char_traits<char>>::operator<<(unsigned long)" from source as ostream_print_ulong_spec with (
+    \this this
+    \prepost{osM} this |-> ostreamR 1$m osM
+    \pre{str} this |-> ostream_contentR 1$m str
+    \arg{n} "" (Vint n)
+    \post[Vptr this]
+        this |-> ostream_contentR 1$m (str ++ Z_to_string n)
+  ).
+
+  Definition iostream_manip_spec state_f contents_f : WpSpec_cpp_val := (
+    \arg{osP : ptr} "" (Vptr osP)
+    (* XXX: manipulators can modify [osM]! *)
+    \pre{osM} osP |-> ostreamR 1$m osM
+    \post* osP |-> ostreamR 1$m (state_f osM)
+    \pre{str} osP |-> ostream_contentR 1$m str
+    \post[Vptr osP] osP |-> ostream_contentR 1$m (contents_f str)).
+
+  Definition ostream_cpp_type : type :=
+    "std::basic_ostream<char, std::char_traits<char>>&".
+  Definition iostream_manip_kind : okind :=
+    tFunction ostream_cpp_type [ostream_cpp_type].
+
+  cpp.spec "std::endl<char, std::char_traits<char>>(std::basic_ostream<char, std::char_traits<char>>&)" from source as endl_spec with (
+    \exact Reduce iostream_manip_spec (fun osM => osM) (fun str => str ++ "\n")%bs
+  ).
+
+  (* This is the overload taking the endl manipulator. *)
+  cpp.spec "std::basic_ostream<char, std::char_traits<char>>::operator<<(std::basic_ostream<char, std::char_traits<char>>&(*)(std::basic_ostream<char, std::char_traits<char>>&))" from source as ostream_insert_string_spec with (
+    \this this
+    \arg{os_f} "" (Vptr os_f)
+    \pre{state_f stream_f}
+      os_f |-> unmaterialized_specR
+        iostream_manip_kind
+        (iostream_manip_spec state_f stream_f)
+    \pre{osM} this |-> ostreamR 1$m osM
+    \post* this |-> ostreamR 1$m (state_f osM)
+    \pre{str} this |-> ostream_contentR 1$m str
+    \post[Vptr this]
+      this |-> ostream_contentR 1$m (stream_f str)
+  ).
+
 End with_cpp.

From 8fa75b4a481a1de677c0014d76fae687e6758b0c Mon Sep 17 00:00:00 2001
From: "Paolo G. Giarrusso" <paolo@skylabs-ai.com>
Date: Wed, 11 Feb 2026 21:44:48 +0100
Subject: [PATCH 05/11] More examples

---
 rocq-brick-libstdcpp/test/dune.inc            | 18 +++++++++
 .../geeks_for_geeks_examples/N12_area.cpp     | 30 +++++++++++++++
 .../test/geeks_for_geeks_examples/N12_area.v  | 37 +++++++++++++++++++
 .../N6_print_sizeof.cpp                       | 31 ++++++++++++++++
 .../N6_print_sizeof.v                         | 29 +++++++++++++++
 5 files changed, 145 insertions(+)
 create mode 100644 rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N12_area.cpp
 create mode 100644 rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N12_area.v
 create mode 100644 rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N6_print_sizeof.cpp
 create mode 100644 rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N6_print_sizeof.v

diff --git a/rocq-brick-libstdcpp/test/dune.inc b/rocq-brick-libstdcpp/test/dune.inc
index ffc3af3..f708dd5 100644
--- a/rocq-brick-libstdcpp/test/dune.inc
+++ b/rocq-brick-libstdcpp/test/dune.inc
@@ -26,6 +26,15 @@
                          (run cpp2v -v %{input} -o N0_hello_world_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
  (alias (name srcs) (deps N0_hello_world.cpp))
 )
+(subdir geeks_for_geeks_examples
+ (rule
+  (targets N12_area_cpp.v)
+  (alias test_ast)
+  (deps (:input N12_area.cpp) (glob_files_rec ../*.hpp) (universe))
+  (action
+                         (run cpp2v -v %{input} -o N12_area_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
+ (alias (name srcs) (deps N12_area.cpp))
+)
 (subdir geeks_for_geeks_examples
  (rule
   (targets N2_input_cpp.v)
@@ -62,6 +71,15 @@
                          (run cpp2v -v %{input} -o N5_swap_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
  (alias (name srcs) (deps N5_swap.cpp))
 )
+(subdir geeks_for_geeks_examples
+ (rule
+  (targets N6_print_sizeof_cpp.v)
+  (alias test_ast)
+  (deps (:input N6_print_sizeof.cpp) (glob_files_rec ../*.hpp) (universe))
+  (action
+                         (run cpp2v -v %{input} -o N6_print_sizeof_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
+ (alias (name srcs) (deps N6_print_sizeof.cpp))
+)
 (subdir geeks_for_geeks_examples
  (rule
   (targets iostream_cpp.v)
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N12_area.cpp b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N12_area.cpp
new file mode 100644
index 0000000..ccbab26
--- /dev/null
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N12_area.cpp
@@ -0,0 +1,30 @@
+// C++ program to find area
+// and perimeter of rectangle
+#include<iostream>
+using namespace std;
+
+// Utility function
+int areaRectangle(int a, int b)
+{
+   int area = a * b;
+   return area;
+}
+
+int perimeterRectangle(int a, int b)
+{
+   int perimeter = 2*(a + b);
+   return perimeter;
+}
+
+// Driver code
+int main()
+{
+  int a = 5;
+  int b = 6;
+  cout << "Area = " <<
+           areaRectangle(a, b) <<
+           endl;
+  cout << "Perimeter = " <<
+           perimeterRectangle(a, b);
+  return 0;
+}
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N12_area.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N12_area.v
new file mode 100644
index 0000000..baf4ec4
--- /dev/null
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N12_area.v
@@ -0,0 +1,37 @@
+Require Import skylabs.auto.cpp.prelude.proof.
+Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.spec.
+
+Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.N12_area_cpp.
+
+Import linearity.
+
+Section with_cpp.
+  Context `{Σ : cpp_logic, σ : genv}.
+
+  Definition area_of_rectangle (side1 side2 : Z) := side1 * side2.
+  Definition perimeter_of_rectangle (side1 side2 : Z) := 2 * (side1 + side2).
+  Definition side1 := 5.
+  Definition side2 := 6.
+
+  cpp.spec "main()" from source as main_spec with (
+    \prepost{osM} _global "std::cout" |-> ostreamR 1$m osM
+    \pre{str} _global "std::cout" |-> ostream_contentR 1$m str
+    \post[Vint 0]
+      _global "std::cout" |-> ostream_contentR 1$m
+        (str ++ "Area = " ++ Z_to_string (area_of_rectangle side1 side2) ++ "\n" ++ "Perimeter = " ++ Z_to_string (perimeter_of_rectangle side1 side2))
+  ).
+
+  cpp.spec "areaRectangle(int, int)" from source inline.
+  cpp.spec "perimeterRectangle(int, int)" from source inline.
+
+  Lemma main_ok : verify?[source] main_spec.
+  Proof.
+    verify_shift; go.
+    iExists (_ : ostreamT → ostreamT), (_ : cstring.t → cstring.t); work with br_erefl; go.
+
+    banish_string_literals.
+    iModIntro.
+    rewrite -!(assoc_L BS.append).
+    work.
+  Qed.
+End with_cpp.
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N6_print_sizeof.cpp b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N6_print_sizeof.cpp
new file mode 100644
index 0000000..8e82db0
--- /dev/null
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N6_print_sizeof.cpp
@@ -0,0 +1,31 @@
+#include <iostream>
+using namespace std;
+
+int main()
+{
+    int integerType;
+    char charType;
+    float floatType;
+    double doubleType;
+
+    // Calculate and Print
+    // the size of integer type
+    cout << "Size of int is: " << sizeof(integerType)
+         << "\n";
+
+    // Calculate and Print
+    // the size of doubleType
+    cout << "Size of char is: " << sizeof(charType) << "\n";
+
+    // Calculate and Print
+    // the size of charType
+    cout << "Size of float is: " << sizeof(floatType)
+         << "\n";
+
+    // Calculate and Print
+    // the size of floatType
+    cout << "Size of double is: " << sizeof(doubleType)
+         << "\n";
+
+    return 0;
+}
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N6_print_sizeof.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N6_print_sizeof.v
new file mode 100644
index 0000000..a11e0ec
--- /dev/null
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N6_print_sizeof.v
@@ -0,0 +1,29 @@
+Require Import skylabs.auto.cpp.prelude.proof.
+Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.spec.
+
+Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.N6_print_sizeof_cpp.
+
+Import linearity.
+
+Section with_cpp.
+  Context `{Σ : cpp_logic, σ : genv}.
+
+  cpp.spec "main()" from source as main_spec with (
+    \prepost{osM} _global "std::cout" |-> ostreamR 1$m osM
+    \pre{str} _global "std::cout" |-> ostream_contentR 1$m str
+    \post[Vint 0]
+      Exists str',
+      _global "std::cout" |-> ostream_contentR 1$m
+        (str ++ str')
+  ).
+
+  Lemma main_ok : verify?[source] main_spec.
+  Proof.
+    verify_shift; go.
+
+    banish_string_literals.
+    iModIntro.
+    rewrite -!(assoc_L BS.append).
+    work.
+  Qed.
+End with_cpp.

From 0db2ef354686f3737020ddacbf997d5fa1b0dfe5 Mon Sep 17 00:00:00 2001
From: "Paolo G. Giarrusso" <paolo@skylabs-ai.com>
Date: Wed, 11 Feb 2026 22:06:47 +0100
Subject: [PATCH 06/11] Rephrase proofs for aggressive hint

---
 .../test/geeks_for_geeks_examples/N12_area.v             | 2 +-
 .../test/geeks_for_geeks_examples/N5_swap.v              | 2 +-
 .../test/geeks_for_geeks_examples/spec.v                 | 9 +++++++++
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N12_area.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N12_area.v
index baf4ec4..0570fac 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N12_area.v
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N12_area.v
@@ -31,7 +31,7 @@ Section with_cpp.
 
     banish_string_literals.
     iModIntro.
-    rewrite -!(assoc_L BS.append).
     work.
+    by rewrite -!(assoc_L BS.append).
   Qed.
 End with_cpp.
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v
index 64b852a..3f06e28 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v
@@ -113,7 +113,7 @@ Sreturn (Some (Eint 0 "int"))]
     iExists (_ : ostreamT → ostreamT), (_ : cstring.t → cstring.t); work with br_erefl; go.
     banish_string_literals.
     iModIntro.
-    rewrite -!(assoc_L BS.append).
     work.
+    by rewrite -!(assoc_L BS.append).
   Qed.
 End with_cpp.
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v
index 87c0ddc..c7e640e 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v
@@ -104,4 +104,13 @@ Section with_cpp.
       this |-> ostream_contentR 1$m (stream_f str)
   ).
 
+  Lemma ostream_contentR_aggressive (os_p : ptr) q str str':
+    os_p |-> ostream_contentR q str ⊢
+    [| str = str' |] -∗
+    os_p |-> ostream_contentR q str'.
+  Proof. work. Qed.
+  Definition ostream_contentR_aggressiveC := [CANCEL] ostream_contentR_aggressive.
+
 End with_cpp.
+
+#[export] Hint Resolve ostream_contentR_aggressiveC : br_hints.

From 8a49d09ad6b08147b723debaedb8e95b6c7ace44 Mon Sep 17 00:00:00 2001
From: "Paolo G. Giarrusso" <paolo@skylabs-ai.com>
Date: Wed, 11 Feb 2026 22:09:24 +0100
Subject: [PATCH 07/11] Improve spec

---
 .../test/geeks_for_geeks_examples/N6_print_sizeof.v  | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N6_print_sizeof.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N6_print_sizeof.v
index a11e0ec..e476f45 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N6_print_sizeof.v
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N6_print_sizeof.v
@@ -8,13 +8,19 @@ Import linearity.
 Section with_cpp.
   Context `{Σ : cpp_logic, σ : genv}.
 
+  Definition newline := "
+"%bs.
+
   cpp.spec "main()" from source as main_spec with (
     \prepost{osM} _global "std::cout" |-> ostreamR 1$m osM
     \pre{str} _global "std::cout" |-> ostream_contentR 1$m str
     \post[Vint 0]
-      Exists str',
       _global "std::cout" |-> ostream_contentR 1$m
-        (str ++ str')
+        (str ++
+        "Size of int is: " ++ Z_to_string 4 ++ newline ++
+        "Size of char is: " ++ Z_to_string 1 ++ newline ++
+        "Size of float is: " ++ Z_to_string 4 ++ newline ++
+        "Size of double is: " ++ Z_to_string 8 ++ newline)
   ).
 
   Lemma main_ok : verify?[source] main_spec.
@@ -23,7 +29,7 @@ Section with_cpp.
 
     banish_string_literals.
     iModIntro.
-    rewrite -!(assoc_L BS.append).
     work.
+    by rewrite -!(assoc_L BS.append).
   Qed.
 End with_cpp.

From ebefe20434905af06a3b2a37c578ac07536f6aaa Mon Sep 17 00:00:00 2001
From: "Paolo G. Giarrusso" <paolo@skylabs-ai.com>
Date: Thu, 12 Feb 2026 17:13:08 +0100
Subject: [PATCH 08/11] Fix numbers

---
 rocq-brick-libstdcpp/test/dune.inc            | 58 ++++++++++++-------
 ...{N0_hello_world.cpp => N1_hello_world.cpp} |  0
 .../{N0_hello_world.v => N1_hello_world.v}    |  2 +-
 .../{N2_input.cpp => N3_input.cpp}            |  0
 .../{N2_input.v => N3_input.v}                |  2 +-
 .../{N3_sum.cpp => N4_sum.cpp}                |  0
 .../{N3_sum.v => N4_sum.v}                    |  2 +-
 .../{N3_sum_a.cpp => N4_sum_a.cpp}            |  0
 .../{N3_sum_a.v => N4_sum_a.v}                |  2 +-
 9 files changed, 42 insertions(+), 24 deletions(-)
 rename rocq-brick-libstdcpp/test/geeks_for_geeks_examples/{N0_hello_world.cpp => N1_hello_world.cpp} (100%)
 rename rocq-brick-libstdcpp/test/geeks_for_geeks_examples/{N0_hello_world.v => N1_hello_world.v} (96%)
 rename rocq-brick-libstdcpp/test/geeks_for_geeks_examples/{N2_input.cpp => N3_input.cpp} (100%)
 rename rocq-brick-libstdcpp/test/geeks_for_geeks_examples/{N2_input.v => N3_input.v} (99%)
 rename rocq-brick-libstdcpp/test/geeks_for_geeks_examples/{N3_sum.cpp => N4_sum.cpp} (100%)
 rename rocq-brick-libstdcpp/test/geeks_for_geeks_examples/{N3_sum.v => N4_sum.v} (97%)
 rename rocq-brick-libstdcpp/test/geeks_for_geeks_examples/{N3_sum_a.cpp => N4_sum_a.cpp} (100%)
 rename rocq-brick-libstdcpp/test/geeks_for_geeks_examples/{N3_sum_a.v => N4_sum_a.v} (98%)

diff --git a/rocq-brick-libstdcpp/test/dune.inc b/rocq-brick-libstdcpp/test/dune.inc
index f708dd5..b4ecf39 100644
--- a/rocq-brick-libstdcpp/test/dune.inc
+++ b/rocq-brick-libstdcpp/test/dune.inc
@@ -19,48 +19,48 @@
 )
 (subdir geeks_for_geeks_examples
  (rule
-  (targets N0_hello_world_cpp.v)
+  (targets N12_area_cpp.v)
   (alias test_ast)
-  (deps (:input N0_hello_world.cpp) (glob_files_rec ../*.hpp) (universe))
+  (deps (:input N12_area.cpp) (glob_files_rec ../*.hpp) (universe))
   (action
-                         (run cpp2v -v %{input} -o N0_hello_world_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
- (alias (name srcs) (deps N0_hello_world.cpp))
+                         (run cpp2v -v %{input} -o N12_area_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
+ (alias (name srcs) (deps N12_area.cpp))
 )
 (subdir geeks_for_geeks_examples
  (rule
-  (targets N12_area_cpp.v)
+  (targets N1_hello_world_cpp.v)
   (alias test_ast)
-  (deps (:input N12_area.cpp) (glob_files_rec ../*.hpp) (universe))
+  (deps (:input N1_hello_world.cpp) (glob_files_rec ../*.hpp) (universe))
   (action
-                         (run cpp2v -v %{input} -o N12_area_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
- (alias (name srcs) (deps N12_area.cpp))
+                         (run cpp2v -v %{input} -o N1_hello_world_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
+ (alias (name srcs) (deps N1_hello_world.cpp))
 )
 (subdir geeks_for_geeks_examples
  (rule
-  (targets N2_input_cpp.v)
+  (targets N3_input_cpp.v)
   (alias test_ast)
-  (deps (:input N2_input.cpp) (glob_files_rec ../*.hpp) (universe))
+  (deps (:input N3_input.cpp) (glob_files_rec ../*.hpp) (universe))
   (action
-                         (run cpp2v -v %{input} -o N2_input_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
- (alias (name srcs) (deps N2_input.cpp))
+                         (run cpp2v -v %{input} -o N3_input_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
+ (alias (name srcs) (deps N3_input.cpp))
 )
 (subdir geeks_for_geeks_examples
  (rule
-  (targets N3_sum_cpp.v)
+  (targets N4_sum_cpp.v)
   (alias test_ast)
-  (deps (:input N3_sum.cpp) (glob_files_rec ../*.hpp) (universe))
+  (deps (:input N4_sum.cpp) (glob_files_rec ../*.hpp) (universe))
   (action
-                         (run cpp2v -v %{input} -o N3_sum_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
- (alias (name srcs) (deps N3_sum.cpp))
+                         (run cpp2v -v %{input} -o N4_sum_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
+ (alias (name srcs) (deps N4_sum.cpp))
 )
 (subdir geeks_for_geeks_examples
  (rule
-  (targets N3_sum_a_cpp.v)
+  (targets N4_sum_a_cpp.v)
   (alias test_ast)
-  (deps (:input N3_sum_a.cpp) (glob_files_rec ../*.hpp) (universe))
+  (deps (:input N4_sum_a.cpp) (glob_files_rec ../*.hpp) (universe))
   (action
-                         (run cpp2v -v %{input} -o N3_sum_a_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
- (alias (name srcs) (deps N3_sum_a.cpp))
+                         (run cpp2v -v %{input} -o N4_sum_a_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
+ (alias (name srcs) (deps N4_sum_a.cpp))
 )
 (subdir geeks_for_geeks_examples
  (rule
@@ -80,6 +80,24 @@
                          (run cpp2v -v %{input} -o N6_print_sizeof_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
  (alias (name srcs) (deps N6_print_sizeof.cpp))
 )
+(subdir geeks_for_geeks_examples
+ (rule
+  (targets N8_ascii_value_cast_cpp.v)
+  (alias test_ast)
+  (deps (:input N8_ascii_value_cast.cpp) (glob_files_rec ../*.hpp) (universe))
+  (action
+                         (run cpp2v -v %{input} -o N8_ascii_value_cast_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
+ (alias (name srcs) (deps N8_ascii_value_cast.cpp))
+)
+(subdir geeks_for_geeks_examples
+ (rule
+  (targets N8_ascii_value_printf_cpp.v)
+  (alias test_ast)
+  (deps (:input N8_ascii_value_printf.cpp) (glob_files_rec ../*.hpp) (universe))
+  (action
+                         (run cpp2v -v %{input} -o N8_ascii_value_printf_cpp.v --no-elaborate  -- -std=c++20 -stdlib=libstdc++ )))
+ (alias (name srcs) (deps N8_ascii_value_printf.cpp))
+)
 (subdir geeks_for_geeks_examples
  (rule
   (targets iostream_cpp.v)
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N0_hello_world.cpp b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N1_hello_world.cpp
similarity index 100%
rename from rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N0_hello_world.cpp
rename to rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N1_hello_world.cpp
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N0_hello_world.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N1_hello_world.v
similarity index 96%
rename from rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N0_hello_world.v
rename to rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N1_hello_world.v
index 21fd44d..2dabb26 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N0_hello_world.v
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N1_hello_world.v
@@ -1,7 +1,7 @@
 Require Import skylabs.auto.cpp.prelude.proof.
 Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.spec.
 
-Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.N0_hello_world_cpp.
+Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.N1_hello_world_cpp.
 
 Section with_cpp.
   Context `{Σ : cpp_logic, σ : genv}.
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N2_input.cpp b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_input.cpp
similarity index 100%
rename from rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N2_input.cpp
rename to rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_input.cpp
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N2_input.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_input.v
similarity index 99%
rename from rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N2_input.v
rename to rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_input.v
index a22b7cb..d911790 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N2_input.v
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_input.v
@@ -1,7 +1,7 @@
 Require Import skylabs.auto.cpp.prelude.proof.
 Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.spec.
 
-Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.N2_input_cpp.
+Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.N3_input_cpp.
 
 Import linearity.
 
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum.cpp b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum.cpp
similarity index 100%
rename from rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum.cpp
rename to rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum.cpp
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum.v
similarity index 97%
rename from rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum.v
rename to rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum.v
index e62a246..fd17459 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum.v
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum.v
@@ -1,7 +1,7 @@
 Require Import skylabs.auto.cpp.prelude.proof.
 Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.spec.
 
-Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.N3_sum_cpp.
+Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.N4_sum_cpp.
 
 Import linearity.
 
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum_a.cpp b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum_a.cpp
similarity index 100%
rename from rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum_a.cpp
rename to rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum_a.cpp
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum_a.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum_a.v
similarity index 98%
rename from rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum_a.v
rename to rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum_a.v
index d6047de..f5bad0c 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N3_sum_a.v
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum_a.v
@@ -1,7 +1,7 @@
 Require Import skylabs.auto.cpp.prelude.proof.
 Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.spec.
 
-Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.N3_sum_a_cpp.
+Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.N4_sum_a_cpp.
 
 Import linearity.
 

From bfbd44949e8f604b2da8c0a2a3e7e87b5aca8086 Mon Sep 17 00:00:00 2001
From: "Paolo G. Giarrusso" <paolo@skylabs-ai.com>
Date: Thu, 12 Feb 2026 17:15:33 +0100
Subject: [PATCH 09/11] Missing URLs

---
 rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum.cpp   | 2 ++
 rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum_a.cpp | 2 ++
 rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.cpp  | 1 +
 3 files changed, 5 insertions(+)

diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum.cpp b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum.cpp
index f0bf9b0..b4c759e 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum.cpp
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum.cpp
@@ -1,3 +1,5 @@
+// https://www.geeksforgeeks.org/cpp/cpp-add-numbers/
+
 #include <iostream>
 using namespace std;
 
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum_a.cpp b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum_a.cpp
index 9323d4c..bbadd7f 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum_a.cpp
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum_a.cpp
@@ -1,3 +1,5 @@
+// https://www.geeksforgeeks.org/cpp/cpp-add-numbers/, 2nd version
+
 #include <iostream>
 using namespace std;
 
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.cpp b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.cpp
index e1e67d6..b3b635d 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.cpp
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.cpp
@@ -1,4 +1,5 @@
 // https://www.geeksforgeeks.org/cpp/cpp-program-to-swap-two-numbers/
+
 #include <iostream>
 using namespace std;
 

From 35944828ff0ceadb5d241596537fd187fc0a576e Mon Sep 17 00:00:00 2001
From: "Paolo G. Giarrusso" <paolo@skylabs-ai.com>
Date: Thu, 12 Feb 2026 17:18:55 +0100
Subject: [PATCH 10/11] fixup! Example 5

---
 .../test/geeks_for_geeks_examples/N5_swap.v   | 75 -------------------
 1 file changed, 75 deletions(-)

diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v
index 3f06e28..3e02a3a 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v
@@ -30,84 +30,9 @@ Section with_cpp.
     \end.
   Next Obligation. work. Qed.
 
-  (* #[program]
-  Definition hint_stream_F :=
-    \cancelx@{mpredI}
-    \bound_existential (stream_f : cstring.t → cstring.t)
-    (* \goal_trigger{os_f : ptr}
-      os_f |-> unmaterialized_specR
-        iostream_manip_kind
-        (iostream_manip_spec stream_f) *)
-    \goal_trigger{os_f : ptr}
-      os_f |-> cptrR
-        iostream_manip_kind
-        (iostream_manip_spec state_f stream_f)
-    \instantiate stream_f := (fun str => str ++ "\n")%bs
-
-    \end.
-  Next Obligation. work. Qed. *)
-
   Lemma main_ok : verify?[source] main_spec.
   Proof.
     verify_shift; go.
-
-(**
-_ : denoteModule source
-_ : ostream_insert_string_spec
-_ : endl_spec
-_ : ostream_print_int_spec
-_ : ostream_insert_spec
-_ : type_ptr "int" a_addr
-_ : type_ptr "int" b_addr
-_ : type_ptr "char" _x_1
-_ : ∀ q : Qp, _x_1 |-> cstring.R q$c "Before swapping a = " ={⊤}=∗ emp
-_ : type_ptr "char" _x_4
-_ : ∀ q : Qp, _x_4 |-> cstring.R q$c " , b = " ={⊤}=∗ emp
---------------------------------------□
-_ : PostCond
-_ : _x_1 |-> cstring.R _x_2$c "Before swapping a = "
-_ : a_addr |-> intR 1$m 2
-_ : _x_4 |-> cstring.R _x_5$c " , b = "
-_ : b_addr |-> intR 1$m 3
---------------------------------------∗
-∃ stream_f : cstring.t → cstring.t,
-_global "std::endl<char, std::char_traits<char>>(std::basic_ostream<char, std::char_traits<char>>&)"
-|-> cptrR
-(unmaterialized_fspec (tFunction ostream_cpp_type [ostream_cpp_type])
-(add_with
-(λ osP : ptr,
-add_arg (Vptr osP)
-(add_with
-(λ osM0 : ostreamT,
-add_pre ([...])
-([...])) "osM" DummyValue)) "osP" DummyValue)) ∗
-(_global "std::cout" |-> ostreamR 1$m osM ∗
-_global "std::cout"
-|-> ostream_contentR 1$m
-(stream_f ((((str ++ "Before swapping a = ") ++ Z_to_string 2) ++ " , b = ") ++ Z_to_string 3)%bs) -∗
-interp source 1
-(interp source ((1 >*> 1) >*> ((1 >*> 1) >*> ((1 >*> 1) >*> (([...]) >*> ([...])))))
-(wp_block source [region: "b" @ b_addr; "a" @ a_addr; return {?: "int"}]
-[Sdecl [Dvar "temp" "int" None]; Sexpr (Eassign (Evar "temp" "int") (Ecast Cl2r ([...])) "int");
-Sexpr (Eassign (Evar "a" "int") (Ecast Cl2r ([...])) "int");
-Sexpr (Eassign (Evar "b" "int") (Ecast Cl2r ([...])) "int");
-Sexpr
-(Eoperator_call OOLessLess
-(operator_impl.MFunc
-"std::basic_ostream<char, std::char_traits<char>>::operator<<(std::basic_ostream<char, std::char_traits<char>>&(*)(std::basic_ostream<char, std::char_traits<char>>&))"%cpp_name
-Direct
-"std::basic_ostream<char, std::char_traits<char>>&(std::basic_ostream<char, std::char_traits<char>>&(*)(std::basic_ostream<char, std::char_traits<char>>&))"%cpp_type)
-[Eoperator_call OOLessLess
-([...])
-[[...];
-[...]];
-Ecast Cfun2ptr
-([...])]);
-Sreturn (Some (Eint 0 "int"))]
-(Kfree source ((1 >*> FreeTemps.delete "int" b_addr) >*> FreeTemps.delete "int" a_addr)
-(Kcleanup source [] (Kreturn ([...])))))))
-*)
-
     (* iExists id, (fun str => str ++ "\n")%bs; go. *)
     iExists (_ : ostreamT → ostreamT), (_ : cstring.t → cstring.t); work with br_erefl; go.
     iExists (_ : ostreamT → ostreamT), (_ : cstring.t → cstring.t); work with br_erefl; go.

From 944dabf8b113528549095524bf0e560f3757da88 Mon Sep 17 00:00:00 2001
From: Gregory Malecha <gregory@skylabs-ai.com>
Date: Thu, 12 Feb 2026 23:56:36 -0500
Subject: [PATCH 11/11] A sketch of a refinement-based setup.

---
 .../test/geeks_for_geeks_examples/spec.v         | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v
index c7e640e..32ac5d1 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v
@@ -30,12 +30,13 @@ Proof. tac_refine. move: H. apply: inj. Qed.
 Section with_cpp.
   Context `{Σ : cpp_logic, σ : genv}.
 
-  Parameter ostreamT : Type.
-  Parameter ostreamR : cQp.t -> ostreamT -> Rep.
-  Parameter ostream_contentR : cQp.t -> cstring.t -> Rep.
+  Parameter ostreamR : cQp.t -> gname -> Rep.
+
+  (** This is effectively an <<AU>> that yields the characters and then continues *)
+  Parameter ostream_yield : gname -> string -> mpred -> mpred.
 
   #[global] Instance: LearnEqF1 ostreamR := ltac:(solve_learnable).
-  #[global] Instance: LearnEqF1 ostream_contentR := ltac:(solve_learnable).
+  (* #[global] Instance: LearnEqF1 ostream_contentR := ltac:(solve_learnable). *)
 
   Parameter istreamT : Type.
   Parameter istreamR : cQp.t -> istreamT -> Rep.
@@ -43,12 +44,11 @@ Section with_cpp.
 
   cpp.spec "std::operator<<<std::char_traits<char>>(std::basic_ostream<char, std::char_traits<char>>&, const char*)" from source as ostream_insert_spec with (
     \arg{osP} "" (Vptr osP)
-    \prepost{osM} osP |-> ostreamR 1$m osM
-    \pre{str} osP |-> ostream_contentR 1$m str
+    \prepost{γ} osP |-> ostreamR 1$m γ
     \arg{strP} "" (Vptr strP)
     \prepost{q__s strM} strP |-> cstring.R q__s strM
-    \post[Vptr osP]
-      osP |-> ostream_contentR 1$m (str ++ strM)).
+    \pre{Q} ostream_yield γ _ Q
+    \post[Vptr osP] Q)
 
   Parameter Z_to_string : Z -> cstring.t.
   #[global] Declare Instance Z_to_string_inj : Inj eq eq Z_to_string.