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?
Kevin's definition would work in Prolog.


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