:- initialization(main).
main :-
sum(b=2,output=Output,a=1),
writeln(Output).
sum(A1,B1,C1) :-
named_args([A1,B1,C1],[a=A,b=B,output=Output]),
Output is A + B.
named_args([],_).
named_args([A|B],C) :-
member(A,C),
named_args(B,C).