### Transposition et réduction du nombre d’altérations accidentelles

Cet exemple, grâce à un peu de code Scheme, donne la priorité aux enharmoniques afin de limiter le nombre d’altérations supplémentaires. La règle applicable est :

• Les altérations doubles sont supprimées
• Si dièse -> Do
• Mi dièse -> Fa
• Do bémol -> Si
• Fa bémol -> Mi

Cette façon de procéder aboutit à plus d’enharmoniques naturelles.

```#(define (naturalize-pitch p)
(let ((o (ly:pitch-octave p))
(a (* 4 (ly:pitch-alteration p)))
;; alteration, a, in quarter tone steps,
;; for historical reasons
(n (ly:pitch-notename p)))
(cond
((and (> a 1) (or (eqv? n 6) (eqv? n 2)))
(set! a (- a 2))
(set! n (+ n 1)))
((and (< a -1) (or (eqv? n 0) (eqv? n 3)))
(set! a (+ a 2))
(set! n (- n 1))))
(cond
((> a 2) (set! a (- a 4)) (set! n (+ n 1)))
((< a -2) (set! a (+ a 4)) (set! n (- n 1))))
(if (< n 0) (begin (set! o (- o 1)) (set! n (+ n 7))))
(if (> n 6) (begin (set! o (+ o 1)) (set! n (- n 7))))
(ly:make-pitch o n (/ a 4))))

#(define (naturalize music)
(let ((es (ly:music-property music 'elements))
(e (ly:music-property music 'element))
(p (ly:music-property music 'pitch)))
(if (pair? es)
(ly:music-set-property!
music 'elements
(map naturalize es)))
(if (ly:music? e)
(ly:music-set-property!
music 'element
(naturalize e)))
(if (ly:pitch? p)
(begin
(set! p (naturalize-pitch p))
(ly:music-set-property! music 'pitch p)))
music))

naturalizeMusic =
#(define-music-function (m)
(ly:music?)
(naturalize m))

music = \relative c' { c4 d e g }

\score {
\new Staff {
\transpose c ais { \music }
\naturalizeMusic \transpose c ais { \music }
\transpose c deses { \music }
\naturalizeMusic \transpose c deses { \music }
}
\layout { }
}
```