; ----

(defun c:nextsheet ( / ix sheet_lst x sheet)
  ; Return the WD_M block's SHEET attribute value
  ; of "next" dwg in project. This embedded in a
  ; global called GBL_wd_prj_ixlst. If global
  ; doesn't exist, make call to refresh it.
  (if (not GBL_wd_prj_ixlst)
    (setq GBL_wd_prj_ixlst (c:ace_proj_data nil)))
  ; GBL_wd_cip holds index of current drawing in
  ; the overall project drawing list. 
  (setq ix GBL_wd_cip) ; index
  ; If index not defined for current drawing, then
  ; trigger a refresh of the global.
  (if (OR (not ix)(= ix 0))
    (setq ix (c:wd_is_cur_dwg_in_proj))
  )
  (setq sheet "")
  (if (> ix 0)
    (progn ; current drawing is in the project,
           ; increment to next dwg in list
      (setq ix (1+ ix)) ; increment index
      ; Get list of SHEET numbers assigned to
      ; all dwgs in the project dwg set.
      (setq sheet_lst (nth 3 GBL_wd_prj_ixlst))
      ; Use index number to pull out the
      ; target drawing's SHEET value. This is
      ; done by first finding the index
      ; number is a list of index numbers
      ; (nth 1 GBL_wd_prj_ixlst), and then
      ; using the position in this list to
      ; pull SHEET number from a parallel list
      ; of sheet numbers in (nth 3 GBL_wd_prj_ixlst)
      (if (setq x (member ix (nth 1 GBL_wd_prj_ixlst)))
        ; found relative position of next
	; dwg's data in parallel lists
        (setq sheet (nth (- (length (nth 1 GBL_wd_prj_ixlst))
			    (length x))
                   (nth 3 GBL_wd_prj_ixlst)))        
      )
  ) )    
  sheet  ; return "" or next SHEET value
)

; ----
(defun c:prevsheet ( / ix sheet_lst x sheet)
  ; Return the WD_M block's SHEET attribute value
  ; of "next" dwg in project. This embedded in a
  ; global called GBL_wd_prj_ixlst. If global
  ; doesn't exist, make call to refresh it.
  (if (not GBL_wd_prj_ixlst)
    (setq GBL_wd_prj_ixlst (c:ace_proj_data nil)))
  ; GBL_wd_cip holds index of current drawing in
  ; the overall project drawing list. 
  (setq ix GBL_wd_cip) ; index
  ; If index not defined for current drawing, then
  ; trigger a refresh of the global.
  (if (OR (not ix)(= ix 0))
    (setq ix (c:wd_is_cur_dwg_in_proj))
  )
  (setq sheet "")
  (if (> ix 1)
    (progn ; current drawing is in the project,
           ; increment to next dwg in list
      (setq ix (1- ix)) ; decrement index
      ; Get list of SHEET numbers assigned to
      ; all dwgs in the project dwg set.
      (setq sheet_lst (nth 3 GBL_wd_prj_ixlst))
      ; Use index number to pull out the
      ; target drawing's SHEET value. This is
      ; done by first finding the index
      ; number is a list of index numbers
      ; (nth 1 GBL_wd_prj_ixlst), and then
      ; using the position in this list to
      ; pull SHEET number from a parallel list
      ; of sheet numbers in (nth 3 GBL_wd_prj_ixlst)
      (if (setq x (member ix (nth 1 GBL_wd_prj_ixlst)))
        ; found relative position of next
	; dwg's data in parallel lists
        (setq sheet (nth (- (length (nth 1 GBL_wd_prj_ixlst))
			    (length x))
                   (nth 3 GBL_wd_prj_ixlst)))        
      )
  ) )    
  sheet  ; return "" or previous SHEET value
)
(princ)