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).

?- [naf].
true.

?- q.
true.

?- \+ s.
true.

?- s.
false.

?- p.
true ;
false.

?- trace.
true.

[trace]  ?- p.
   Call: (10) p ? creep
   Call: (11) q ? creep
   Call: (12) s ? creep
   Call: (13) w ? creep
   Fail: (13) w ? creep
   Fail: (12) s ? creep
   Redo: (11) q ? creep
   Exit: (11) q ? creep
   Call: (11) r ? creep
   Call: (12) t ? creep
   Exit: (12) t ? creep
   Fail: (11) r ? creep
   Redo: (10) p ? creep
   Exit: (10) p ? creep
true .

[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).

?- [beach].
true.

?- away_from_beach.
true.

?- beach_access.
false.

?- assert(on_beach).  % this dynamically states a fact is true
true.

?- away_from_beach.
false.

?- beach_access.
true.

?- assert(enclosed_bay).
true.

?- beach_access.
true.

?- swim_at_beach.
true.

?- assert(big_city).
true.

?- swim_at_beach.
false.

?- assert(in_BC).
true.

?- swim_at_beach.
true.

?- assert(p(a)).
ERROR: No permission to modify static procedure `p/1'
ERROR: Defined at /Users/poole/World/cs312/2024/prolog/beach.pl:30
ERROR: In:
ERROR:   [10] assert(p(a))
ERROR:    [9] toplevel_call('<garbage_collected>') at /opt/local/lib/swipl/boot/toplevel.pl:1173
?- ^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).

?- (3+4)=7.
false.

?-