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).

?- [simpeg].
true.

?- trace.
true.

[trace]  ?- a
|    .
   Call: (10) a ? creep
   Call: (11) b ? creep
   Call: (12) f ? creep
   Call: (13) j ? creep
   Call: (14) c ? creep
   Call: (15) e ? creep
   Exit: (15) e ? creep
   Exit: (14) c ? creep
   Exit: (13) j ? creep
   Call: (13) e ? creep
   Exit: (13) e ? creep
   Exit: (12) f ? creep
   Call: (12) k ? creep
   Fail: (12) k ? creep
   Redo: (12) f ? abort
% Execution Aborted
[trace]  ?- notrace.
true.

[debug]  ?- nodebug.
true.

?- [simpeg].
true.

?- a
|    .
ERROR: Stack limit (1.0Gb) exceeded
ERROR:   Stack sizes: local: 1.0Gb, global: 37Kb, trail: 0Kb
ERROR:   Stack depth: 7,892,177, last-call: 0%, Choice points: 7,892,170
ERROR:   Probable infinite recursion (cycle):
ERROR:     [7,892,177] user:b
ERROR:     [7,892,176] user:a
ERROR:     [7,892,175] user:b
   Exception: (7,888,985) b ? abort
% Execution Aborted
?- ^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.

?- trace.
true.

[trace]  ?- father(pierre,Y), parent(Y,Z).
   Call: (11) father(pierre, _13530) ? creep
   Exit: (11) father(pierre, justin) ? creep
   Call: (11) parent(justin, _13536) ? creep
   Call: (12) mother(justin, _13536) ? creep
   Fail: (12) mother(justin, _13536) ? creep
   Redo: (11) parent(justin, _13536) ? creep
   Call: (12) father(justin, _13536) ? creep
   Exit: (12) father(justin, xavier) ? creep
   Exit: (11) parent(justin, xavier) ? creep
Y = justin,
Z = xavier ;
   Redo: (12) father(justin, _13536) ? Unknown option (h for help)
   Redo: (12) father(justin, _13536) ? creep
   Exit: (12) father(justin, ella_grace) ? creep
   Exit: (11) parent(justin, ella_grace) ? creep
Y = justin,
Z = ella_grace ;
   Redo: (11) father(pierre, _13530) ? creep
   Exit: (11) father(pierre, alexandre) ? creep
   Call: (11) parent(alexandre, _13536) ? creep
   Call: (12) mother(alexandre, _13536) ? creep
   Fail: (12) mother(alexandre, _13536) ? creep
   Redo: (11) parent(alexandre, _13536) ? creep
   Call: (12) father(alexandre, _13536) ? creep
   Fail: (12) father(alexandre, _13536) ? creep
   Fail: (11) parent(alexandre, _13536) ? creep
   Redo: (11) father(pierre, _13530) ? creep
   Exit: (11) father(pierre, michel) ? creep
   Call: (11) parent(michel, _13536) ? creep
   Call: (12) mother(michel, _13536) ? creep
   Fail: (12) mother(michel, _13536) ? creep
   Redo: (11) parent(michel, _13536) ? creep
   Call: (12) father(michel, _13536) ? creep
   Fail: (12) father(michel, _13536) ? creep
   Fail: (11) parent(michel, _13536) ? creep
false.

[trace]  ?-