structure Nat = 

 struct

 datatype nat = Suc of nat | Zero_nat;

 fun eqop_nat Zero_nat Zero_nat = true

   | eqop_nat (Suc m) (Suc n) = eqop_nat m n

   | eqop_nat Zero_nat (Suc a) = false

   | eqop_nat (Suc a) Zero_nat = false;

 end; (*struct Nat*)

 structure List = 

 struct

 fun null (x :: xs) = false

   | null [] = true;

 fun list_all2 p (x :: xs) (y :: ys) = p x y andalso list_all2 p xs ys

   | list_all2 p xs [] = null xs

   | list_all2 p [] ys = null ys;

 end; (*struct List*)

 structure Codegen = 

 struct

 datatype monotype = Mono of Nat.nat * monotype list;

 fun eqop_monotype (Mono (tyco1, typargs1)) (Mono (tyco2, typargs2)) =

   Nat.eqop_nat tyco1 tyco2 andalso

     List.list_all2 eqop_monotype typargs1 typargs2;

 end; (*struct Codegen*)