exists p.to_map
α : Type
n first last : Nat
arr arr' : Vec α n
p : permuted n first last arr arr'
⊢ ∃ f, invertible f ∧ ∀ (i : Fin n), arr[i] = arr'[f i]
α : Type
n first last : Nat
arr arr' : Vec α n
p : permuted n first last arr arr'
⊢ invertible p.to_map ∧ ∀ (i : Fin n), arr[i] = arr'[p.to_map i]