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(pascal).
false.

?- language(prolog).
true.

?- language(X).
X = smalltalk .

?- language(L).
L = smalltalk ;
L = lisp ;
L = prolog.

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

?- essence(lisp,DT,CF).
DT = lists,
CF = 'recursive functions'.

?- essence(prolog,DT,_).
DT = relations.

?- essence(prolog,_,CF).
CF = 'logical inferencing'.

?- essence(L,objects,_).
L = smalltalk.

?- history(lisp,I,_).
I = inventor('John McCarth').

?- history(lisp,inventor(Name),_).
Name = 'John McCarth'.

?- history(_,inventor(N),_),write(N),nl,fail.
Alan Kay
John McCarth
Alan Colmeraur
false.

?- halt