The subject formula includes the object formula.
Formula A includes formula B if there exists some substitution
which when applied to B creates a formula B' such that for
every statement in B' is also in A, every variable
universally (or existentially) quantified in B' is quantified in
the same way in A.
Variable substitution is applied recursively to nested compound terms such as
formulae, lists and sets.
(Understood natively by cwm when in in the antecedent of a rule.
You can use this to peer inside nested formulae.)