Euclid's algorithm
                finding 
		the greatest common divider (gcd)
           	and 
		the least common multiple (lcm) of two integers.

		?- gcd(6,15,X).
	   	X = 3
		?- lcm(6,7,Y).
		Y = 42
		?- lcm(16,14,R).
		R = 112
    
		gcd(X,0,X).
		gcd(X,Y,D):- R is X mod Y, gcd(Y,R,D).

		lcm(X,Y,M):- gcd(X,Y,D),M is (X*Y)/D.