Script started on XXX XXX XX 11:48:19 XXXX

 > cat g1.p

       snt --> det(F), adjs(F), noun.
       det(F) --> [a], { F = consonant } ;
                   [an], { F = vowel }.
       adjs(F) --> adj(F); adj(F), adjs(_).
       adj(F) --> [spotted], { F = consonant } ;
                  [endangered], { F = vowel } ;
                  [poison_arrow], { F = consonant }.
       noun --> [frog] ; [owl].

 > pl

Welcome to SWI-Prolog (Multi-threaded, Version 5.6.24)
Copyright (c) 1990-2006 University of Amsterdam.
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to redistribute it under certain conditions.
Please visit http://www.swi-prolog.org for details.

For help, use ?- help(Topic). or ?- apropos(Word).

?- ['g1.p'].

% g1.p compiled 0.01 sec, 3,152 bytes

Yes
?- snt(X,[]).

X = [a, spotted, frog] ;

X = [a, spotted, owl] ;

X = [a, poison_arrow, frog] ;

X = [a, poison_arrow, owl] ;

X = [a, spotted, spotted, frog] ;

X = [a, spotted, spotted, owl] ;

X = [a, spotted, endangered, frog] ;

X = [a, spotted, endangered, owl] ;

X = [a, spotted, poison_arrow, frog] ;

X = [a, spotted, poison_arrow, owl] 

Yes

?- snt([an|X], []).

X = [endangered, frog] ;

X = [endangered, owl] ;

X = [endangered, spotted, frog] ;

X = [endangered, spotted, owl] ;

X = [endangered, endangered, frog] ;

X = [endangered, endangered, owl] ;

X = [endangered, poison_arrow, frog] ;

X = [endangered, poison_arrow, owl] ;

X = [endangered, spotted, spotted, frog] ;

X = [endangered, spotted, spotted, owl] ;

X = [endangered, spotted, endangered, frog] 

Yes

?- Det = an, snt([Det | Rest], []), X = [Det|Rest].

Det = an
Rest = [endangered, frog]
X = [an, endangered, frog] ;

Det = an
Rest = [endangered, owl]
X = [an, endangered, owl] ;

Det = an
Rest = [endangered, spotted, frog]
X = [an, endangered, spotted, frog] ;

Det = an
Rest = [endangered, spotted, owl]
X = [an, endangered, spotted, owl] ;

Det = an
Rest = [endangered, endangered, frog]
X = [an, endangered, endangered, frog] ;

Det = an
Rest = [endangered, endangered, owl]
X = [an, endangered, endangered, owl] ;

Det = an
Rest = [endangered, poison_arrow, frog]
X = [an, endangered, poison_arrow, frog] ;

Det = an
Rest = [endangered, poison_arrow, owl]
X = [an, endangered, poison_arrow, owl] ;

Det = an
Rest = [endangered, spotted, spotted, frog]
X = [an, endangered, spotted, spotted, frog] ;

Det = an
Rest = [endangered, spotted, spotted, owl]
X = [an, endangered, spotted, spotted, owl] ;

Det = an
Rest = [endangered, spotted, endangered, frog]
X = [an, endangered, spotted, endangered, frog] ;

Det = an
Rest = [endangered, spotted, endangered, owl]
X = [an, endangered, spotted, endangered, owl] 

Yes

?- halt.

 > exit
 >

script done on XXX XXX XX 11:51:40 XXXX