$ gprolog GNU Prolog 1.2.8 By Daniel Diaz Copyright (C) 1999-2001 Daniel Diaz | ?- consult('socrates.pro'). compiling /home/Zaxo/socrates.pro for byte code... /home/Zaxo/socrates.pro compiled, 6 lines read - 382 bytes written, 61 ms yes | ?- mortal(socrates). yes | ?- mortal(V). V = socrates yes | ?- mortal(aristotle). no | ?- halt. $