% Example based on Page 85 (Section 2.13.2) of Sebesta
mother(joanne, jake).
father(vern, joanne).
grandparent(X, Z):-parent(X, Y), parent(Y, Z).

% the following definition of parent was not on page 84
parent(X,Y):-father(X,Y); mother(X,Y).

% commands excuted before run starts:
:- nl,nl,print('Examples to try'),nl.
:- print('    father(bob, darcie).'),nl.
:- print('    grandparent(vern, jake).'),nl,nl.