anchor.diff:  
   // Optimization ---------------------------------------------------------------
   
  +// Remove 'this' bindings from lambdas when it is not used in body
  +let RemoveUnusedThis expr =
  +    let bound = HashSet()
  +    let rec rem expr =
  +        match expr with
  +        | Lambda (Some this, args, body) -> 
  +            bound.Add this |> ignore
  +            let bodyTr = Transform rem body
  +            if bound.Contains this then
  +                 bound.Remove this |> ignore
  +                 Lambda (None, args, bodyTr)
  +            else
  +                 Lambda (Some this, args, bodyTr)
  +        | Var v when bound.Contains v ->
  +            bound.Remove v |> ignore
  +            expr
  +        | _ -> Transform rem expr  
  +
  +    rem expr
  +
   /// Transforms local Let- or LetRecursive-bound curried lambda functions to
   /// multi-argument functions when such transformations are possible - the
   /// functions are strictly local, do not escape the scope, and are always
  
positive.code:     let step expr =
          match expr with
          | Application (Lambda (None, args, body), xs) ->
              if List.length args = List.length xs then
                  let bind key value body = Let (key, value, body)
                  List.foldBack2 bind args xs body
              else expr
          | Application (Let (var, value, body), xs) ->
              Let (var, value, Application (body, xs))
          | Lambda (None, [x], Application (Var f, [Var y])) when x = y ->
              Var f
          | Let (var, Let (v, vl, bd), body) ->
              Let (v, vl, Let (var, bd, body))
          | Let (var, value, body) when not var.IsMutable ->
              match value with
              | Constant _ | Global _ | Runtime ->
  
negative.code: let Optimize expr =
      expr
      |> AlphaNormalize
      |> RemoveUnusedThis
      |> Uncurry
      |> RemoveLoops
      |> CollectObjLiterals
      |> Simplify
  
  // Elaboration ----------------------------------------------------------------
  