subst(TV,T) :- equals(TV, T), not occurs(TV, T), not typeVar(T), typeVar(TV).

equals(A, pointer(TP, subst(TV, T)))
:- equals(A, TP), subst(TV, T), not typeVar(TP), occurs(TV, TP).

type(pointer(TP, subst(TV, T)), Name, Num)
:- type(TP, Name, Num), subst(TV, T), occurs(TV, TP).

param(pointer(TP, subst(TV, T)), Param, PNum)
:- type(pointer(TP, subst(TV, T)), Name, Num), subst(TV, T), param(TP, Param, PNum), not occurs(TV, Param).

param(pointer(TP, subst(TV, T)), pointer(Param, subst(TV, T)), PNum)
:- type(pointer(TP, subst(TV, T)), Name, Num), subst(TV, T), param(TP, Param, PNum), occurs(TV, Param).