a + of_num b = 10 : Prop
@eq.{1} nat (@add.{1} nat nat_has_add ((λ (x : nat), x) a) (nat.of_num b))
  (@bit0.{1} nat nat_has_add
     (@bit1.{1} nat nat_has_one nat_has_add (@bit0.{1} nat nat_has_add (@one.{1} nat nat_has_one)))) :
  Prop