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

?- language(snobol).
true.

?- language(snowball).
false.

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

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

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

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

?- history(_, inventor(Name), _).
Name = 'Alan Kay' .

?- history(N, _, date(1959)).
N = lisp.

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

?- halt.