This member is added by an implicit conversion from SubsumptionTheory to
any2stringadd[SubsumptionTheory] performed by method any2stringadd in scala.Predef.
This member is added by an implicit conversion from SubsumptionTheory to
StringFormat[SubsumptionTheory] performed by method StringFormat in scala.Predef.
Background theory that only validates clauses that are subsumed by axioms.