diff --git a/rocq-brick-libstdcpp/test/dune.inc b/rocq-brick-libstdcpp/test/dune.inc
index a5b255d..b4ecf39 100644
--- a/rocq-brick-libstdcpp/test/dune.inc
+++ b/rocq-brick-libstdcpp/test/dune.inc
@@ -19,21 +19,84 @@
 )
 (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 N2_input_cpp.v)
+  (targets N1_hello_world_cpp.v)
   (alias test_ast)
-  (deps (:input N2_input.cpp) (glob_files_rec ../*.hpp) (universe))
+  (deps (:input N1_hello_world.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 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 N3_input_cpp.v)
+  (alias test_ast)
+  (deps (:input N3_input.cpp) (glob_files_rec ../*.hpp) (universe))
+  (action
+                         (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 N4_sum_cpp.v)
+  (alias test_ast)
+  (deps (:input N4_sum.cpp) (glob_files_rec ../*.hpp) (universe))
+  (action
+                         (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 N4_sum_a_cpp.v)
+  (alias test_ast)
+  (deps (:input N4_sum_a.cpp) (glob_files_rec ../*.hpp) (universe))
+  (action
+                         (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
+  (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 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 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
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..0570fac
--- /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.
+    work.
+    by rewrite -!(assoc_L BS.append).
+  Qed.
+End with_cpp.
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/N4_sum.cpp b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum.cpp
new file mode 100644
index 0000000..b4c759e
--- /dev/null
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum.cpp
@@ -0,0 +1,13 @@
+// https://www.geeksforgeeks.org/cpp/cpp-add-numbers/
+
+#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/N4_sum.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum.v
new file mode 100644
index 0000000..fd17459
--- /dev/null
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_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.N4_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$m (str ++ Z_to_string 20)
+  ).
+
+  Lemma main_ok : verify?[source] main_spec.
+  Proof. verify_spec; go. Qed.
+End with_cpp.
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum_a.cpp b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum_a.cpp
new file mode 100644
index 0000000..bbadd7f
--- /dev/null
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum_a.cpp
@@ -0,0 +1,20 @@
+// https://www.geeksforgeeks.org/cpp/cpp-add-numbers/, 2nd version
+
+#include <iostream>
+using namespace std;
+
+int main() {
+    int a = 11, b = 9;
+
+    // If b is positive, increment a to b times
+    for (int i = 0; i < b; i++)
+        a++;
+
+    // If b is negative, decrement a to |b| times
+    for (int i = 0; i > b; i--)
+        a--;
+
+    cout << a;
+
+    return 0;
+}
diff --git a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum_a.v b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum_a.v
new file mode 100644
index 0000000..f5bad0c
--- /dev/null
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N4_sum_a.v
@@ -0,0 +1,37 @@
+Require Import skylabs.auto.cpp.prelude.proof.
+Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.spec.
+
+Require Import skylabs.brick.libstdcpp.test.geeks_for_geeks_examples.N4_sum_a_cpp.
+
+Import linearity.
+
+Section with_cpp.
+  Context `{Σ : cpp_logic, σ : genv}.
+
+  cpp.spec "main()" from source as main_spec with (
+    \prepost{osM} _global "std::cout" |-> ostreamR 1$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.
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..b3b635d
--- /dev/null
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.cpp
@@ -0,0 +1,18 @@
+// 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..3e02a3a
--- /dev/null
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N5_swap.v
@@ -0,0 +1,44 @@
+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"
+      )
+  ).
+
+  #[program]
+  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.
+
+  Lemma main_ok : verify?[source] main_spec.
+  Proof.
+    verify_shift; 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.
+    work.
+    by rewrite -!(assoc_L BS.append).
+  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..e476f45
--- /dev/null
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/N6_print_sizeof.v
@@ -0,0 +1,35 @@
+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}.
+
+  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$m str
+    \post[Vint 0]
+      _global "std::cout" |-> ostream_contentR 1$m
+        (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.
+  Proof.
+    verify_shift; go.
+
+    banish_string_literals.
+    iModIntro.
+    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 bcc48b1..32ac5d1 100644
--- a/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v
+++ b/rocq-brick-libstdcpp/test/geeks_for_geeks_examples/spec.v
@@ -16,19 +16,27 @@ 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.
 
+#[global] Arguments BS.append : simpl never.
+
 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.
@@ -36,12 +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.
@@ -56,4 +63,54 @@ 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)
+  ).
+
+  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.