Re: where do I think wrong

On 2014-03-17 01:24, Richard A. O'Keefe wrote:
> On 15/03/2014, at 12:03 AM, Kilian Evang wrote:
>>>> >>>    half_or_full_siblings(X, Y) :-
>>>>> >>>>        (   same_father(X, Y),
>>>>> >>>> 	    X \== Y
>>>>> >>>> 	;   same_mother(X, Y),
>>>>> >>>> 	    \+ same_father(X, Y)
>>>>> >>>> 	).
>> > 
>> > Because you don't usually want to say that a person is his or her own
>> > sibling.
>> > 
>> > What I don't understand is why the X \== Y is only in the first
>> > or-branch. IMHO it should also be in the second.
> It would be utterly pointless in the second clause.
> It is subsumed by the \+ same_father(X, Y) test;
> you certainly have the same father as yourself!

D'oh, of course. Silly me.

Kilian