mul2(X1,X0,Y1,Y0,M3,M2,M1,M0) :-
	cell(0,  0,  X0,Y0,M0,C00),
	cell(0,  0,  X1,Y0,S10,C10)
	&&
	cell(S10,C00,X0,Y1,M1, C01),
	cell(0  ,C10,X1,Y1,S11,C11)
	&&
	cell(S11,C01,0, 0,M2 , M3),
	cell(0,  C11,0, 0, _, _  ).


cell(Sin,Cin,X,Y,Sout,Cout) :-
	and(X,Y,L1),S1 <- Sin,C1<- Cin
	&&
	full_adder(S1,C1,L1,Sout,Cout).

full_adder(S1,C1,L1,Sout,Cout) :-
	half_adder(S1,C1,S2,C2),L2 <- L1
	&&
	half_adder(S2,L2,S3,C3),
	C4 <- C2
	&&
	or(C3,C4,Cout),
	Sout <- S3.

half_adder(A,B,S,C) :-
	length(1),
	A = 0, B = 0,
	@S = 0, @C = 0.
half_adder(A,B,S,C) :-
	length(1),
	A = 0, B = 1,
	@S = 1, @C = 0.
half_adder(A,B,S,C) :-
	length(1),
	A = 1, B = 0,
	@S = 1, @C = 0.
half_adder(A,B,S,C) :-
	length(1),
	A = 1, B = 1,
	@S = 0, @C = 1.

or(A,B,C) :-
	length(1),
	A = 0, B = 0,
	@C = 0.
or(A,B,C) :-
	length(1),
	A = 0, B = 1,
	@C = 1.
or(A,B,C) :-
	length(1),
	A = 1, B = 0,
	@C = 1.
or(A,B,C) :-
	length(1),
	A = 1, B = 1,
	@C = 1.

and(A,B,C) :-
	length(1),
	A = 0, B = 0,
	@C = 0.
and(A,B,C) :-
	length(1),
	A = 0, B = 1,
	@C = 0.
and(A,B,C) :-
	length(1),
	A = 1, B = 0,
	@C = 0.
and(A,B,C) :-
	length(1),
	A = 1, B = 1,
	@C = 1.

test1 :-
	mul2(1,1,1,1,M3,M2,M1,M0),

 	fin(write((M3,M2,M1,M0))),
 	keep(write((M3,M2,M1,M0))).