?- consult('prolang.pro').
true.

?- language(snobol).
true.

?- language(snowball).
false.

?- essence(snobol,DT,_).
DT = pattern.

?- essence(_,arrays,_).
false.

?- language(Language).
Language = smalltalk ;
Language = lisp ;
Language = prolog ;
Language = snobol ;
Language = apl.

?- language(Language),write(language),nl,fail.
language
language
language
language
language
false.

?- language(Language),write(Language),nl,fail.
smalltalk
lisp
prolog
snobol
apl
false.

?- history(apl,inventor(Inventor),_).
Inventor = 'Kenneth Iverson'.

?- history(_,inventor(Name),_).
Name = 'Alan Kay' ;
Name = 'John McCarthy' ;
Name = 'Alan Comeraur' ;
Name = 'Ralph Griswold' ;
Name = 'Kenneth Iverson'.

?- history(_,inventor(Name),_),write(Name),nl,fail.
Alan Kay
John McCarthy
Alan Comeraur
Ralph Griswold
Kenneth Iverson
false.

?- history(Language,_,date(1959)),essence(Language,lists,_).
Language = lisp .