:-op(550, xfy, :).
sum_cl(empty, 0).
sum_cl(Head:Tail, Sum) :- sum_cl(Tail,TailSum), Sum is Head + TailSum.

member_cl(Value, :(Value,_)).
member_cl(Value, :(_,Tail)) :- member_cl(Value, Tail).

%sum_cl(empty, 0).
%sum_cl(cell(Head,Tail), Sum) :- sum_cl(Tail,TailSum), Sum is Head + TailSum.

cl(1,cell(10, cell(20, cell(30, empty)))).
/*
cell(10,
    cell(20,
	    cell(30, empty)))).
*/

