if hji : j = i then
  cases hji; simp only [ite_true]
else
  rw [if_neg hji, if_pos rfl]
case mk.mk
α : Type u
x : Subarray α
i : Nat
hi : i < size x
j : Nat
hj : j < size x
⊢ (if j = i then x[i] else if i = i then x[j] else x[i]) = x[j]
no goals