anchor.diff:    "Add LUMP to BPN. MAX-N-STRIPES of LUMP gets set to equal that of
     the previous last, non-weight lump of BPN."
     (when (find-lump (name lump) bpn)
  -    (error "Cannot add ~S: ~%
  +    (error "Cannot add ~S: ~
               a lump of same name has already been added to this network." lump))
     (setf (max-n-stripes lump) (max-n-stripes bpn))
     (vector-push-extend lump (slot-value bpn 'lumps) 1)
  
positive.code: 
  (defun ensure-+-ones (lump)
    (let ((n-stripes* (n-stripes* lump)))
      (unless (and (ones lump)
                   (= n-stripes*
                      (mat-size (ones lump))))
        (setf (slot-value lump 'ones)
              (make-mat n-stripes* :ctype flt-ctype))
        (fill! (flt 1) (ones lump))))
    (ones lump))
  
  (defmethod transfer-lump ((lump ->+))
    (let* ((nodes (nodes lump))
  
negative.code: (defun ensure-mask (lump)
    (when (dropout lump)
      (let ((x (nodes (x lump))))
        (setf (slot-value lump 'mask)
              (if (mask lump)
                  (adjust! (mask lump) (mat-size x) 0)
                  (make-mat (mat-size x) :ctype flt-ctype)))))
    (mask lump))
  
  (define-cuda-kernel (cuda-dropout-xorwow)
  