Set: pp::colors
  Set: pp::unicode
  Assumed: vec
  Assumed: concat
  Assumed: concat_assoc
  Assumed: empty
  Assumed: concat_empty
∀ (n : ℕ) (v : vec (n + 0)) (w : vec n), v = w ; empty
loop3.lean:20: error: executing script
error: bad argument #3 to 'simplify' (options expected)
STEP 1
STEP 2
λ n : ℕ, ∃ (v : vec (n + 0)) (w : vec n), v ≠ w ; empty
====>
λ n : ℕ, ∃ v x : vec n, v ≠ x