transitive closure

csaba1 (csaba1@umbc.edu)
Wed, 5 Mar 2003 10:08:35 -0500

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Hi,

The transitive closure has to be modified to work for the ancestor
relationship
the following way:

closure(R)(X,Y) :- R(X,Y).
closure(R)(X,Y) :- R(Z,Y),closure(R)(X,Z).

this will translate to
ancestor(X,Y) :- parent(X,Y). (if X is parent of Y, X is Y's ancestor)
ancestor(X,Y) :- parent(Z,Y),ancestor(X,Z). (find Y's parent first, then check
if X is the ancestor of Y's parent)

I really don't know why the original definition does not work. Any ideas?
(I always thought this "fixed" version was more intutitive anyways)

BTW. I am not getting any e-mails sent to the class mailing list (I read the
question on the website). Anybody else has this problem?

Csaba

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