anchor.diff:                                        (setf processes (remove process processes))
                                         (return-from per-pattern process))))
                                   processes)
  -                          (error 'unification-failure)))
  +                          (error 'unification-failure
  +                                 :format-control "Could not unify ~s with any process in ~s"
  +                                 :format-arguments (list pattern processes))))
                         patterns)
                 substitutions)
  -        (error 'unification-failure))))
  +        (error 'unification-failure
  +               :format-control "Can not unify two different length lists: ~s ~s"
  +               :format-arguments (list patterns processes)))))
   (defgeneric match-down (pattern process &optional substitutions))
   (defgeneric match-up (pattern process &optional substitutions))
   (defgeneric match-kell (pattern process &optional substitutions)
  
positive.code:                                     (push process matched-processes)
                                      (return-from per-pattern process)))))
                              (gethash (name pattern) processes))
                        (error 'unification-failure)))
                    patterns)
            substitutions)))
  
  
negative.code:                                   (setf processes (remove process processes))
                                    (return-from per-pattern process))))
                              processes)
                        (error 'unification-failure
                               :format-control "Could not unify ~s with any process in ~s"
                               :format-arguments (list pattern processes))))
                    patterns)
            substitutions)))
  
  