The assertions (Θ) the top level conjunction carries.
Whether the conjunction contradicts itself - one variable asserted to be two distinct terms, or a
conjunct that folded to false. Such a filter is the empty operation.
What is left of the condition once the assertions are taken out of it, with the strong ones
substituted into it (FReord), or undefined when the assertions are all there was.
What the top level conjunction of a filter condition says about the variables, cached on the filter the way CPMeta is cached on any operation.