Bach geometra?

Trascrizione del meraviglioso Canone 1 a 2 dell'"Offerta musicale" di J. S. Bach (1747) ad uso didattico (la funzione proviene da http://dvoi.com/files/lilypond/2.5.3/Documentation/user/out-www/lilypond/Manipulating-music-expressions.html)

\version "2.12.3"


\paper {

}

\header {
title = \markup \center-column {\fontsize #6.0 "Bach's Crab Canon" \line { } }
}


#(define (reverse-music music)
(let* ((elements (ly:music-property music 'elements))
(reversed (reverse elements))
(e (ly:music-property music 'element))
(span-dir (ly:music-property music 'span-direction)))

(ly:music-set-property! music 'elements reversed)

(if (ly:music? e)
(ly:music-set-property!
music 'element
(reverse-music e)))

(if (ly:dir? span-dir)
(ly:music-set-property! music 'span-direction (- span-dir)))

(map reverse-music reversed)

music))


frase = \relative c' {
%\clef treble
%\key c \minor
%\time 4/4

c2 ees | g aes |
b, r4 g'4~ | g fis2 f4~ |
f e2 ees4~ | ees d des c |
b g c f | ees2 d | %9
c ees | g8 f g c g ees d ees |
f g a b c ees, f g | aes d, ees f g f ees d |
ees f g aes bes aes g f | g aes bes c des bes aes g |
a b c d ees c b a | b c d ees f d g, d' | %17
c d ees f ees d c b | c4 g ees c
}

pausa =\relative c {
%\clef treble
%\key c \minor
%\time 4/4

s1 | s1 |
s1 | s1 |
s1 | s1 |
s1 | s1 |
s1 | s1 |
s1 | s1 |
s1 | s1 |
s1 | s1 |
s1 | s1 |

}



\score {
\new PianoStaff <<
%\set PianoStaff.instrumentName = #"Piano "
\new Staff = "upper" {
\clef treble
\key c \minor
\time 4/4
\frase
\pausa
\applyMusic #reverse-music \frase
\bar "|."
}
\new Staff = "lower" {
\clef treble
\key c \minor
\time 4/4
\pausa
\applyMusic #reverse-music \frase
\frase
}
>>
\layout {

}
\midi {

}
}

Ecco il pdf: http://git.phc.unipi.it/presentazione/preslily/blobs/raw/ec22b5076b79fbc3631993613a92cf0ac8943011/Esempi/canon_crab.pdf

Stampando le 18 battute su una striscia di carta (le prime nove verso, le altre 9 retro) come in http://www.youtube.com/watch?v=xUHQ2ybTejU ed incollando propriamente le due estremità si ottiene un esempio musicale del Nastro di Möbius