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                     an example code for Prolog
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klim@moose:~/tmp> gprolog 
GNU Prolog 1.3.0
By Daniel Diaz
Copyright (C) 1999-2007 Daniel Diaz
| ?- [pp].
compiling /home/klim/tmp/pp.pl for byte code...
/home/klim/tmp/pp.pl compiled, 25 lines read - 2165 bytes written, 17 ms

yes

| ?- father(terach,issac).              +-------------------------------+    
                                        | father(terach, abraham).      |
no                                      | father(terach, nachor).       |
| ?- father(terach,haran).              | father(terach, haran).        |
                                        |                               |
yes                                     | father(haran,lot).            |
| ?- father(terach,X).                  | father(haran,milcah).         |
                                        | father(haran,yiscah).         |
X = abraham ? ;                         |                               |
                                        | mother(sarah, isaac).         |
X = nachor ? ;                          |                               |
                                        | male(terach).                 |
X = haran                               | male(abraham).                |
                                        | male(nachor).                 |
yes                                     | male(haran).                  |
| ?- father(X,abraham).                 | male(isaac).                  |
                                        | male(lot).                    |
X = terach ? ;                          | male(sarah).                  |
                                        | male(yiscah).                 |
no                                      |                               |
| ?- father(X,Y).                       | parent(X,Y) :- father(X,Y).   |
                                        | parent(X,Y) :- mother(X,Y).   |
X = terach                              |                               |
Y = abraham ? ;                         | son(X,Y) :-                   |
                                        |   parent(Y,X), male(X).       |
..........................              | daughter(X,Y) :-              |
                                        |   parent(Y,X), female(X).     |
yes                                     +-------------------------------+
| ?- parent(X,nachor).

X = terach ? ;

no
| ?- append([1], [2,3], X).             +-------------------------------+   
                                        | append([], X, X).             |
X = [1,2,3]                             | append([X|Xs], Y, [X|Z]) :-   |
                                        |   append(Xs, Y, Z).           |
yes                                     +-------------------------------+
| ?- append(X,Y,[1,2,3]).  

X = []
Y = [1,2,3] ? ;

X = [1]
Y = [2,3] ? ;

X = [1,2]
Y = [3] ? ;

X = [1,2,3]
Y = [] ? ;

no
| ?-