mba:assignment2 johnz$ swipl
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(L).
L = smalltalk ;
L = lisp ;
L = prolog ;
L = snobol ;
L = apl.

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

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

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

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

?- essence(_,lists,_),history(_,_,date(1959)).
true.