🚀 go-pugleaf

In article <270@ininx.UUCP>, jkreznar@ininx.UUCP (John E. Kreznar) writes:
> What's a good way to represent sets of (possibly non-ground) terms in a setting
> where terms are regarded as identical if they are variants of one another?

> But if variable-name correspondence between terms in the set _is_ important, as
> for example if it's a set of atoms within a clause, this device will not work.
> For example, the equivalence of the sets
> 		{p(X, a), p(Y, b)} and
> 		{p(U, b), p(V, a)}
> does not seem to be easily detectable.

A lot of Prolog coding problems are eased by using redundant representations.
For this particular problem, the thing that springs to mind is representing
each term by a _pair_ of terms, one the grounded version of the other.  So
a set of terms might be stored as a list of Ground-Original pairs, sorted
on Ground.  That would give us
	[p('$VAR'(0),a)-p(X,a), p('$VAR'(0),b)-p(Y,b)]
	[p('$VAR'(0),a)-p(V,a), p('$VAR'(0),b)-p(U,b)]
for which equivalence _is_ easily detectable.

Of course, as variables become instantiated, the Ground versions become
inappropriate, so it would be best to compute the Ground versions just
before using them.
-- 
You can lie with statistics ... but not to a statistician.