case a.zero =>
  rw [String.decEq_refl a]; simp
  constructor <;> try constructor <;> try constructor
  intros p
  contradiction
a : String
⊢ Ø ⋁
    ¬ₛ
      (match String.decEq a a with
          | isTrue h => O
          | isFalse h => _ a)↗ =ₛ
        O
no goals