/* facts */
set_height(dave, 180).
set_height(alice, 155).
set_height(bob, 176).
set_height(mary, 166).
set_height(phi, 166).
set_height(tom, 32).

/* rules */
taller_than(X, Y) :- set_height(X, XH), set_height(Y, YH), XH < YH.
smaller_than(X, Y) :- set_height(X, XH), set_height(Y, YH), XH > YH.
same_height(X, Y) :- set_height(X, XH), set_height(Y, YH), XH = YH.
size(X) :- set_height(X, XH), write(X), write(' is '), write(XH), write(' cm tall!').