need

   1 Action::RemoveValue
   2         RemoveBoundValue
   3 ? KnownFactSet
   4 ? KnownResolutionSet
   5 Predicate::Foreach
   6 Predicate::Findall
   7 Predicate::Forall
   8 Predicate::Rule
   9 Predicate::Not
  10 Step::SubSolve
  11 Solution
  12 Endjinn