:- op(300, fx, dummyop).

dummyop 2.

%
% typical desk
%
def_object desk.

		% default vaules for number, size of drawers
	d_len(70).	% drawer length
	d_num(3).	% drawer number
	d_width(30).	% drawer width

		% drawer total area - general rule
	d_tot_area(R) :-
		self::d_num(Num),
		self::d_len(Len),
		self::d_width(Width),
		R is Num*Len*Width.

end_def desk.

%
% my desk has an extra drawer
%
def_object my_desk
	isa desk.

	d_num(4).	% overrides "default" defn

end_def my_desk.

%
% his desk has shorter drawers
%
def_object his_desk
	isa desk.

	d_len(50).	% overrides "default" defn

end_def his_desk.

%
% typical???? room
%
def_object room.

	d_area(T) :-
		my_desk::d_tot_area(A1),
		his_desk::d_tot_area(A2),
		T is A1 + A2.

end_def room.