type 'a substitution = (int * 'a foterm) list
-type comparison = Lt | Eq | Gt | Incomparable
+type comparison = Lt | Eq | Gt | Incomparable | Invertible
type rule = Superposition | Demodulation
type 'a passive_clause = int * 'a unit_clause (* weight * equation *)
+val is_eq_clause : 'a unit_clause -> bool
+val vars_of_term : 'a foterm -> int list
+
module M : Map.S with type key = int
type 'a bag = int (* max ID *)