q10280621600 subst_functor/2

subst_functor(X, X) :- atomic(X).
subst_functor(X, Y) :-
    X =.. [f, ArgX],
    Y =.. [h, ArgY],
    subst_functor_list([ArgX], [ArgY]).
subst_functor(X, Y) :-
    X =.. [g, ArgX1, ArgX2],
    Y =.. [g, ArgY1, ArgY2],
    subst_functor_list([ArgX1, ArgX2], [ArgY1, ArgY2]).
subst_functor_list([], []).
subst_functor_list([H1|T1], [H2|T2]) :-
    subst_functor(H1, H2),
    subst_functor_list(T1, T2).