> On Jan 31, 2018, at 2:15 PM, George Neuner <gneun...@comcast.net> wrote:
> On 1/31/2018 2:10 PM, Sam Caldwell wrote:
>> Your definition of `ancestor` is one or two steps of parentage:
>> > ancestor(A, B) :- parent(A, B).
>> > ancestor(A, B) :-
>>       parent(A, C),
>>       parent(C, B).
>> I suspect you want one of those lines to appeal to the `ancestor` relation 
>> to allow longer chains.
> Knowing nothing about datalog he asks naively:
> Shouldn't the rule    ancestor(A, B) :- parent(A, C), parent(C, B).   be 
> applied recursively?

It is — except that there’s no recursion. 

> Kevin's definition would work in Prolog.

No it wouldn’t. 

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