Идеологически более верная.

g(Text,Word) :-
member(Word, Text), not(disjoinable(Text,Word)), not(better_word(Text,Word)).

disjoinable(Text,Word) :-
member(NewWord, Text), disj_word(Word,NewWord).

disj_word([],Word).
disj_word([Head|Tail],NewWord) :-
not(member(Head,NewWord)), disj_word(Tail,NewWord).

better_word(Text,Word) :-
len(Word,Len),
member(AnotherWord, Text), 
AnotherWord \= Word,
not(disjoinable(Text,AnotherWord)),
len(AnotherWord, AnotherLen), 
Len > AnotherLen.

len([],0).
len([H|T], Len) :- len(T,Len1), Len is Len1+1.