use a 1
case refine_2
n : ℕ
hn : Squarefree n
a : Fin 3 → ℕ
ha : a ∈ finMulAntidiagonal 3 n
⊢ (a 0 * a 1, a 0 * a 2).2 ∣ a 0 * a 1 * a 2
case h
n : ℕ
hn : Squarefree n
a : Fin 3 → ℕ
ha : a ∈ finMulAntidiagonal 3 n
⊢ a 0 * a 1 * a 2 = (a 0 * a 1, a 0 * a 2).2 * a 1