formula subclass of expression.

How did I get this far without noticing that?
composite-formula is a subclass of formula.

Another surprise.
Generic predicates for determining whether something is a generalization.
Free occurrence.
Continue with the instantiation.
Generic predicates for moves related to generalizations.
Rulesets now have validators.
Wrong use of instantiation.
D and E validators.
Use the validators.
Paranoia: check whether the new moves make sense.
Use the E FOL validator.