TFL/mask.sig

little improvement for the handling of sort constraints:
two non-identical explicit constriants are considered equal if they give
the same set in different enumerations, e.g. {term,ord,ord} = {ord,term}

signature Mask_sig =
sig
 datatype 'a binding = |-> of ('a * 'a)  (* infix 7 |->; *)

 type mask
 val ERR : mask

end