Re: General question about better documentation and specific question

[Vic Bancroft]

n Sat, 1 Dec 2001, Violetta Cavalli-Sforza wrote:

> Thank you. One more question and then I'll stop asking for a while.

You breathe life into the list . . . 

> I have the following database of facts and rules. 
> ...
> 
> can_marry(X,Y) :- X \= Y, not(sibling(X,Y)), not(cousin(X,Y)).

This definition seem a little lax, even fore the west coast ;>

  /usr/home/bancroft/src/prolog/can_marry.pl compiled, 
  32 lines read - 3708 bytes written, 193 ms

  (20 ms) yes
  | ?- can_marry( john, mary ).
  can_marry( john, mary ).

  yes

Since this theory of wedding seems to permit any pair except those 
that match any in a list of exceptions. You might consider,

  ok_marry( X, Y ) :- \+ forbidden( X, Y ). 

Then one simply lists the exceptions, as so,

  forbidden( X, X ).
  forbidden( X, Y ) :- parent( X, Y ).
  forbidden( X, Y ) :- cousin( X, Y ).
  forbidden( X, Y ) :- sibling( X, Y ).

Of course, this does still allow :

  | ?- ok_marry( albert, ann ).
  ok_marry( albert, ann ).

  yes

Soo, perhaps one could just introduce the ancestor relation,

  ancestor( X, Y ) :- parent( X, Y ).
  ancestor( X, Y ) :- parent( X, Z ), parent( Z, Y ).

A fairly recently lost taboo one might have conventionally considered,

  same_sex( X, Y ) :- father( X, _ ), father( Y, _ ).
  same_sex( X, Y ) :- mother( X, _ ), mother( Y, _ ).

> ... (though this definition comes straight out of Clocksin and
> Mellish).

That is a classic text!  Perhaps as you work through the examples, we 
could build up a gprolog FAQ section on the _Clocksin and Mellish_ 
examples . . . who are the gprolog FAQ maintainers ?

more,
l8r,


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 Victor Bancroft
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 Athens, Georgia  30602, U.S.A           http://ai.uga.edu/~bancroft
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