Turns a Rete.IR.CompoundNegation into something a Rete network can express.

Internal. A negation node watches one condition, and propagates its token while nothing matches. It cannot watch a conjunction. De Morgan's law does not rescue it here: the conjuncts share existentially quantified variables. With orders {1} and refunds {2}, "no x has both" is true, and the rewrite is false.

So the conjunction is lifted into a generated helper that inserts a marker fact, and the compound negation becomes an ordinary negation of that marker:

defrule clean({:customer, cid}, {:nand, [{:order, cid}, {:refund, cid}]})

# becomes, in effect
defrule clean__neg_1({:customer, cid}, {:order, cid}, {:refund, cid}) do
  {:"clean__neg_1", %{cid: cid}}
end
defrule clean({:customer, cid}, {:not, [{:"clean__neg_1", cid}]})

Three things make that correct.

The marker carries the bindings the conjunction joins on. Otherwise, one customer with both an order and a refund would suppress the rule for every customer. The helper repeats the preceding conditions, which is what binds those variables. The helper also fires first, through an :internal_salience set to the nesting depth. So extraction chains correctly, and the negating rule never observes an absence that had merely not been computed yet.

A helper's expressions are plain closures, because extraction runs at build time, long after macro expansion. See docs/design/network.md §6.