show sign (x.inv ^ (k+1 : Nat)) = 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 (inv x ^ (k + 1)) = false