retract

abstract override fun retract(clause: Clause): RetractResult<ProblogTheory>
abstract override fun retract(clauses: Iterable<Clause>): RetractResult<ProblogTheory>
abstract override fun retract(clauses: Sequence<Clause>): RetractResult<ProblogTheory>
open override fun retract(head: Struct): RetractResult<ProblogTheory>