poole@CPSC-M-POOLE01 prolog % swipl
Welcome to SWI-Prolog (threaded, 64 bits, version 9.0.4)
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software.
Please run ?- license. for legal details.

For online help and background, visit https://www.swi-prolog.org
For built-in help, use ?- help(Topic). or ?- apropos(Word).

?- [backeg].
true.

?- trace.
true.

[trace]  ?- a.
   Call: (10) a ? creep
   Call: (11) b ? creep
   Exit: (11) b ? creep
   Call: (11) c ? creep
   Call: (12) s ? creep
   Exit: (12) s ? creep
   Exit: (11) c ? creep
   Call: (11) d ? creep
   Call: (12) f ? creep
   Fail: (12) f ? creep
   Fail: (11) d ? creep
   Redo: (11) c ? creep
   Call: (12) t ? creep
   Exit: (12) t ? creep
   Exit: (11) c ? creep
   Call: (11) d ? creep
   Call: (12) f ? creep
   Fail: (12) f ? creep
   Fail: (11) d ? creep
   Redo: (10) a ? creep
   Call: (11) e ? creep
   Call: (12) t ? creep
   Exit: (12) t ? creep
   Exit: (11) e ? creep
   Exit: (10) a ? creep
true ;
   Redo: (11) e ? creep
   Call: (12) s ? abort
% Execution Aborted
[trace]  ?- ^D
% halt
poole@CPSC-M-POOLE01 prolog % swipl
Welcome to SWI-Prolog (threaded, 64 bits, version 9.0.4)
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software.
Please run ?- license. for legal details.

For online help and background, visit https://www.swi-prolog.org
For built-in help, use ?- help(Topic). or ?- apropos(Word).

?- [family].
true.

?- grandmother(X,xavier).
X = margaret ;
X = estelle ;
false.

?- grandmother(X,pierre).
false.

?- [elect_reln].
true.

?- up(X).
X = s2 ;
X = s3.

?- live(X).
X = w2 ;
X = l2 ;
X = w4 ;
X = p1 ;
X = w3 ;
X = p2 ;
X = w6 ;
X = w5 ;
X = outside.

?- connected_to(A,B).
A = l1,
B = w0 ;
A = w0,
B = w1 ;
A = w2,
B = w3 ;
A = l2,
B = w4 .

?-