57

Author: datokrat

HumanEvalLean/HumanEval57.lean

@@ -1,7 +1,30 @@
 module
 
-def monotonic : Unit :=
-  ()
+/-! ## Implementation -/
+
+def monotonic (xs : List Int) : Bool :=
+  xs.Pairwise (· ≤ ·) || xs.Pairwise (· ≥ ·)
+
+/-! ## Tests -/
+
+set_option cbv.warning false
+
+example : monotonic [1, 2, 4, 10] = true := by cbv
+example : monotonic [1, 2, 4, 20] = true := by cbv
+example : monotonic [1, 20, 4, 10] = false := by cbv
+example : monotonic [4, 1, 0, -10] = true := by cbv
+example : monotonic [4, 1, 1, 0] = true := by cbv
+example : monotonic [1, 2, 3, 2, 5, 60] = false := by cbv
+example : monotonic [1, 2, 3, 4, 5, 60] = true := by cbv
+example : monotonic [9, 9, 9, 9] = true := by cbv
+
+/-! ## Verification -/
+
+theorem monotonic_iff :
+    monotonic xs ↔
+      (∀ (i j : Nat) (hi : i < j) (hj : j < xs.length), xs[i] ≤ xs[j]) ∨
+      (∀ (i j : Nat) (hi : i < j) (hj : j < xs.length), xs[i] ≥ xs[j]) := by
+  grind [monotonic, List.pairwise_iff_getElem]
 
 /-!
 ## Prompt
@@ -47,4 +70,4 @@ def check(candidate):
     assert candidate([9, 9, 9, 9]) == True
 
 ```
--/
+-/