simp
case a
a b : String
n : ℕ
ab : a = b
⊢ ∀ (n : ℕ),
    Ø ⋁
      ((match isTrue (_ : b = b) with
          | isTrue h => fromNat n
          | isFalse h => _ b) +ₛ
          match isTrue (_ : b = b) with
          | isTrue h => fromNat n
          | isFalse h => _ b) =ₛ
        (match isTrue (_ : b = b) with
          | isTrue h => fromNat n
          | isFalse h => _ b) +ₛ
          match isTrue (_ : b = b) with
          | isTrue h => fromNat n
          | isFalse h => _ b
case a
a b : String
n : ℕ
ab : a = b
⊢ ∀ (n : ℕ), Ø ⋁ fromNat n +ₛ fromNat n =ₛ fromNat n +ₛ fromNat n