Welcome to SWI-Prolog (threaded, 64 bits, version 8.0.3)
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software.
Please run ?- license. for legal details.

For online help and background, visit http://www.swi-prolog.org
For built-in help, use ?- help(Topic). or ?- apropos(Word).

?- consult('proglang.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.
smalltalk
lisp
prolog
snobol
apl
false.

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

?- history(_,inventor(I),_).
I = 'Alan Kay' ;
I = 'John McCarth' ;
I = 'Alan Colmeraur' ;
I = 'Ralph Griswold' ;
I = 'Kenneth Iverson'.

?- history(_,inventor(I),_),write(I),nl,fail.
Alan Kay
John McCarth
Alan Colmeraur
Ralph Griswold
Kenneth Iverson
false.

?- history(_,_,1959),essence(_,list,_).
false.

?- halt.