(defun ask-upcase-word-backward ( ) 
         "Description: upcase-word-backward" 
         (interactive) (upcase-word -1))
(defun ask-downcase-word-backward ( ) 
         "Description: downcase-word-backward" 
         (interactive) (downcase-word -1))
(defun ask-cap-word-backward ( ) 
         "Description: capitalize-word-backward" 
         (interactive) (capitalize-word -1))
(global-set-key (kbd "s-u") 'ask-upcase-word-backward)
(global-set-key (kbd "s-c") 'ask-cap-word-backward)
(global-set-key (kbd "s-l") 'ask-downcase-word-backward)

;; s- means pressing "super-key" of a window symbol.