structure S where
  carrier : Type
  mul : carrier → carrier → carrier

def Nat.S : S where
  carrier := Nat
  mul := (· * ·)

def Int.S : S where
  carrier := Int
  mul := (· * ·)

unif_hint (s : S) where
  s =?= Nat.S ⊢ s.carrier =?= Nat

unif_hint (s : S) where
  s =?= Int.S ⊢ s.carrier =?= Int

def mul {s : S} (a b : s.carrier) : s.carrier :=
  s.mul a b

def square (x : Nat) : Nat :=
  mul x x

set_option pp.all true
#print square

#check fun x : Nat => mul x x

#check fun y : Int => mul y y

def BV (n : Nat) := { a : Array Bool // a.size = n }

def sext (x : BV s) (n : Nat) : BV (s+n) :=
  ⟨mkArray (s+n) false, Array.size_mkArray ..⟩

def bvmul (x y : BV w) : BV w :=
  x

unif_hint (x : Nat) where
  x =?= 64 ⊢ Nat.add 64 x =?= 128

set_option pp.all false

def tst (x y : BV 64) : BV 128 :=
  bvmul (sext x 64) (sext y _)