We often want to write rules that fire when we have a certain number of
facts that meet some criteria.  If I am trying to write a rule that
fires on a certain cardinality, it isn't very straightforward.

We can write a rule that will try to keep a count of the number of facts
that meet a certain template.

We can write a rule that matches on a specific number (using
constraints).  We write a number of these rules, one for each number we
are looking for.

Jess supports the (count-query-results) function, which can be helpful
but can't really be used on the left side of a rule.

Some variant on the logical support mechanism might be feasible here.

So what is the best mechanism for counting facts that meet a pattern,
then using that count to drive rules?

RJ

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