intro i
case right
α : Type
n first last : Nat
arr arr' : Vec α n
p : permuted n first last arr arr'
⊢ ∀ (i : Fin n), arr[i] = arr'[p.to_map i]
case right
α : Type
n first last : Nat
arr arr' : Vec α n
p : permuted n first last arr arr'
i : Fin n
⊢ arr[i] = arr'[p.to_map i]