anchor.diff:           *)
           let ctx = model.Context
           let destE = mkIntLV ctx dest
  -        ( [makeRel model srcE destE],
  -          new Set<string> ( [ flattenLV dest ] ))
  +        [makeRel model srcE destE]
       | BoolLocalSet (dest, srcE) ->
           let ctx = model.Context
           let destE = mkBoolLV ctx dest
  -        ( [makeRel model srcE destE],
  -          new Set<string> ( [ flattenLV dest ] ))
  +        [makeRel model srcE destE]
       | PrimId ->
  -        ( [ctx.MkTrue ()], Set.empty)
  +        [ctx.MkTrue ()]
       | PrimAssume (assumption) ->
           // Assumes always only refer to the pre-state.
  -        ( [subAllInModel model envVarToBefore (assumption :> Expr) :?> BoolExpr],
  -          Set.empty)
  +        [subAllInModel model envVarToBefore (assumption :> Expr) :?> BoolExpr]
  
positive.code:     | ArithFetch (dest, src, mode) -> makeArithFetch model dest src mode
      | BoolFetch (dest, src) -> makeBoolFetch model dest src
      | ArithCAS (dest, test, set) ->
          (makeCAS model
                   (mkIntLV ctx dest :> Expr)
                   (mkIntLV ctx test :> Expr)
                   set,
           new Set<string> ( [ flattenLV dest
                               flattenLV test ] ))
      | BoolCAS (dest, test, set) ->
          (makeCAS model
                   (mkBoolLV ctx dest :> Expr)
                   (mkBoolLV ctx test :> Expr)
                   set,
           new Set<string> ( [ flattenLV dest
                               flattenLV test ] ))
      | ArithLocalSet (dest, srcE) ->
          (* By the meta-theory, this and BoolLocalSet can be modelled
           * similarly to atomic fetches.
  
negative.code:     (* We have to use Some and List.collect to ensure that the term
       * for dest is only included if there actually _is_ a dest.
       *)
      [// If dest exists, create dest!after = src!before.
       Option.map (makeRel model srcE) destE
       // Create src!after = F(src!before), where F is
       // defined by the fetch mode.
       makeFetchUpdate model srcE mode |> Some]
      |> List.choose id
  
  /// Emits a Boolean fetch.
  let makeBoolFetch model dest src =
  