% Fractions and rational numbers in Prolog gcd(X,X,X):-!. gcd(X,1, 1):-!. gcd(1,X,1):-!. gcd(X,0, X):-!. gcd(0,X,X):-!. gcd(X,Y,Z):-X>Y,!, XY is X mod Y, gcd(XY,Y,Z). gcd(X,Y,Z):-X