anchor.diff:      // defining views is to be held true.
       match (findDefOfView dvs ms) with
           | Some _ ->
  -            lift2 (fun cR msR -> ite cR msR True)
  -                  (boolExpr c)
  -                  (predOfMultiset env (marker >> ok) tryArithExpr ms)
  -        | None -> ok True
  +            Some (lift2 (fun cR msR -> ite cR msR True)
  +                    (boolExpr c)
  +                    (predOfMultiset env (marker >> ok) tryArithExpr ms))
  +        | None -> None
   
   /// Constructs the body for a set of condition pair Horn clauses,
   /// given the defining views, preconditions and semantics clause.
  
positive.code: /// command semantics, as well as a globals environment.
  let hsfConditionSingle dvs env q body =
      lift (fun qH -> { Head = qH ; Body = body })
           (hsfGuarMultiset dvs env aAfter q)
  
  /// Constructs a series of Horn clauses for a term.
  /// Takes the environment of active global variables.
  
negative.code:     let psH =
          ps
          |> Multiset.toSeq
          |> Seq.choose (hsfGuarMultiset dvs env aBefore)
          |> collect
          |> lift List.ofSeq
  
  