diff --git a/docs/BUILTINS.md b/docs/BUILTINS.md
index 376f5e5..ba9dc64 100644
--- a/docs/BUILTINS.md
+++ b/docs/BUILTINS.md
@@ -618,4 +618,4 @@ receiver.
 
 | Name | Signature | Description |
 |------|-----------|-------------|
-| `__borrow_guard_selftest` | `__borrow_guard_selftest of [args...]` | **Not a user builtin.** A planted fault validating the #548 borrow-scan guard: registered only in ASan builds when `EIGS_BORROW_GUARD_SELFTEST` is set, it deliberately returns a borrowed direct child past `VM_BORROW_SCAN_CAP` so the suite can prove the guard aborts loudly (naming the builtin) instead of letting a missed compensating incref become a silent use-after-free. Absent from release builds and from sanitizer builds without the opt-in env var (fuzzers must never reach a deliberate abort). |
+| `__borrow_guard_selftest` | `__borrow_guard_selftest of [args...]` | **Not a user builtin.** A planted fault validating the #548 borrow-scan guard: registered only in ASan builds when `EIGS_BORROW_GUARD_SELFTEST` is set, it deliberately returns a borrowed direct child past `VM_BORROW_SCAN_CAP` so the suite can prove the guard aborts loudly (naming the builtin) instead of letting a missed compensating incref become a silent use-after-free. Absent from release builds and from sanitizer builds without the opt-in env var (fuzzers must never reach a deliberate abort). |   
diff --git a/docs/STDLIB.md b/docs/STDLIB.md
index 9ab99b3..a337013 100644
--- a/docs/STDLIB.md
+++ b/docs/STDLIB.md
@@ -58,7 +58,8 @@ signature comment above each function (e.g., `# clamp of [value, lo, hi]`).
 | `lcm` | `lcm of [a, b]` | Least common multiple |
 | `argmax` | `argmax of list` | Index of the largest element (first on ties, -1 if empty) |
 | `argmin` | `argmin of list` | Index of the smallest element (first on ties, -1 if empty) |
-
+| `log2` | `log2 of x` | base-2 logarithm |
+| `log10` | `log10 of x` | base-10 logarithm |
 ### lib/list.eigs — Functional List Operations
 
 | Function | Signature | Description |
diff --git a/lib/math.eigs b/lib/math.eigs
index 2457528..20cd035 100644
--- a/lib/math.eigs
+++ b/lib/math.eigs
@@ -135,3 +135,12 @@ define argmin(items) as:
             best_val is items[i]
             best_idx is i
     return best_idx
+
+# ---- log2: base-2 logarithm ----
+define log2(x) as:
+    return (log of x) / 0.6931471805599453
+
+# ---- log10: base-10 logarithm ----
+define log10(x) as:
+    return (log of x) / 2.302585092994046
+