n : ℕ
⊢ ↑(-1) = n
n : ℕ
⊢ val (-1) = n
dsimp [val, Fin.coe_neg]
case zero

⊢ ↑(-1) = Nat.zero

case succ
n✝ : ℕ
⊢ ↑(-1) = Nat.succ n✝
n : ℕ
⊢ ↑(-1) = n
cases n
no goals
case zero

⊢ ↑(-1) = Nat.zero
simp [Nat.mod_one]
case succ
n✝ : ℕ
⊢ ↑(-1) = Nat.succ n✝
case succ
n✝ : ℕ
⊢ ↑(-1) = Nat.succ n✝
dsimp [ZMod, ZMod.cast]
no goals
case succ
n✝ : ℕ
⊢ ↑(-1) = Nat.succ n✝
rw [Fin.coe_neg_one]