anchor.diff:                   (error "No binding for ~A in or above ~A" symbol env))))
         (error "No binding for ~A in or above ~A" symbol env)))
   
  -(defmethod (setf lookup) (new-value symbol (env env))
  +(defun (setf lookup) (new-value symbol &optional (env *global-env*))
     (when (eq symbol *ignore*)
       (error "Attempted to set #ignore in ~A" env))
     (if env
  
positive.code:             t))
        nil))
  
  (defmethod extend ((env env) symbol &optional value)
    (assert (clutter-symbol-p symbol))
    (unless (eq symbol *ignore*)
      (when (nth-value 1 (gethash symbol (env-bindings env)))
  
negative.code: 
  (declaim (optimize debug))
  
  (defstruct (env (:constructor make-env (&rest parents)))
    parents
    (bindings (make-hash-table :test 'eq)))
  
  (defmethod print-object ((o env) s)
    (print-unreadable-object (o s :type t :identity t)
  