Subterm defined using univ

Source: The Art of Prolog

Program source code: subterm_2.pl

/*
   subterm(Sub,Term) :- Sub is a subterm of the ground term Term.
*/
     subterm(Term,Term).
     subterm(Sub,Term) :- 
        compound(Term), Term =.. [F|Args], subterm_list(Sub,Args).
 
     subterm_list(Sub,[Arg|Args]) :- 
        subterm(Sub,Arg).
     subterm_list(Sub,[Arg|Args]) :-
	subterm_list(Sub,Args).
 
%  Program 9.4   Subterm defined using univ