(om::defmethod! no-voice-crossing ((voices list) (input-mode t) &optional (rule-type :true/false) (weight 1))
 :initvals '( (0 1) :all :true/false 1)
 :indoc '("voices-list"  "input-mode" "rule-type" "weight-number")
 :icon 180 ; THIS IS THE NUMBER OF THE QUESTION MARK ICON FOR OM
 :menuins '( (1 (("all" :all) ("beat" :beat) ("1st-beat" :1st-beat) ("1st-voice" :1st-voice) ))
                    (2 (("true/false" :true/false) ("heur-switch" :heur-switch)) )
                 ) 
 :doc 	 "Voices should not cross, i.e., the pitch of simultaneous note pairs in voices are always sorted in decreasing order.

Arguments are inherited from rpitch-pitch." 

;NOTE: I've changed the name r-pitch-pitch to rpitch-pitch when porting CE to OM (This is also true for all CE functions). The original function (r-pitch-pitch) still exists in CE package as a ordinary lisp function (without the OM interface generated by om::defmethod!).

(let ((sorted-voices (sort voices #'<))
       (rule (eval `#'(lambda (pitches) ;MOVED THE RULE HERE TO AVOID LEXICAL CLOSURES
                             (apply #'>= (remove NIL pitches))))))   ;; no rests -- no NILs
  (mappend #'(lambda (voice1 voice2)
   (ce::r-pitch-pitch
    rule ;<== THE VARIABLE RULE CREATED BY LET 
    voices
    '(0)
    input-mode 
    nil ;<==  gracenotes?: no grace-notes available in OM
    :pitch
    rule-type weight))
    (butlast sorted-voices) 
    (rest sorted-voices))))