. show sign (x ^ (k : Nat)) = false
  exact sign_powNat_of_even x k h
case ofNat
m n : Nat
x : Permutation n
h : sign x = false
k : Nat
⊢ sign (x ^ Int.ofNat k) = false

case negSucc
m n : Nat
x : Permutation n
h : sign x = false
k : Nat
⊢ sign (x ^ Int.negSucc k) = false
case negSucc
m n : Nat
x : Permutation n
h : sign x = false
k : Nat
⊢ sign (x ^ Int.negSucc k) = false