anchor.diff:  
   (defun make-operation-method-lambda (task-var task-input-vars task-inputs chain-var body environment)
     "Create a method lambda that will be used for a method added to the
  -  PERFORM-OPERATION generic function. The resulting method added akin to
  -  the method lambda created when evaluating the following DEFMETHOD
  +PERFORM-OPERATION generic function. The resulting method lambda is
  +similar to the method lambda created when evaluating the following
  +DEFMETHOD
   
  -  `(let ((#:task-inputs ',task-input-classes))
  -     (defmethod perform-operation ((,task-var ,task-class) #:chain)
  -       (destructuring-bind ,task-input-vars
  -           (obtain-task-inputs #:chain (class-of ,task-var) #:task-input-classes)
  -         ,@body))))
  +`(let ((#:task-inputs ',task-input-classes))
  +   (defmethod perform-operation ((,task-var ,task-class) #:chain)
  +     (destructuring-bind ,task-input-vars
  +         (obtain-task-inputs #:chain (class-of ,task-var) #:task-input-classes)
  +       ,@body))))
   
  -  Note that the TASK-CLASS above is not used in
  -  MAKE-OPERATION-METHOD-LAMBDA. It is however used in MAKE-OPERATION-METHOD.
  +Note that the TASK-CLASS above is not used in
  +MAKE-OPERATION-METHOD-LAMBDA. It is however used in
  +MAKE-OPERATION-METHOD.
  +
  +Like CLOSER-MOP:MAKE-METHOD-LAMBDA, this function should be invoked
  +within a macro and the result used in the returned expression.
  +
  +See DEFINE-OPERATION on how to use this function correctly.
   "
     (let ((gf (ensure-generic-function 'perform-operation)))
       (closer-mop:make-method-lambda
  
positive.code: 	(chain-var (gensym)))
      (multiple-value-bind (method-lambda initialisation-arguments)
  	(make-operation-method-lambda task-var task-input-vars task-inputs chain-var body env)
        `(ensure-operation ',task-var
  			 (find-class ',task-class)
  			 ',chain-var
  			 (function ,method-lambda)
  			 ',initialisation-arguments))))
  
negative.code: 	   :function method-lambda
  	   initialisation-arguments)))
  
  (defun ensure-operation (method)
    "Add METHOD to the PERFORM-OPERATION generic function."
    (let ((gf (ensure-generic-function 'perform-operation)))
      (add-method gf method)))
  
  (defmacro define-operation ((task-var task-class) (&rest task-inputs) &body body &environment env)
    "Define the operation to be performed for the TASK-CLASS. All task
  inputs are defined with TASK-INPUTS.
  
  e.g.
  (define-operation (task my-task) ((input task-input))
    (compute-solution (rho task) input)
  "
    (let ((task-input-vars (mapcar #'first task-inputs))
  	(task-inputs (mapcar #'(lambda (x)
  				 `(find-task-input ',(second x)))
  