trying to define microtonal note names and accidentals

[Stefan Thomas]

Dear community,
I'm trying to define microtonal note names and accidentals with the HE-font.
Unfortunately, I get the following error message when I compile the below
quoted file:

> error: wrong type for argument 2.  Expecting
> music, found "c"
> Music = \relative
>                  c' {ch2 cl }
> /home/stefan/partituren/vorlagen/snippet_stefansMikrotoene.ly:65:20:
> error: syntax error, unexpected '''
> Music = \relative c
>                   ' {ch2 cl }
> /home/stefan/partituren/vorlagen/snippet_stefansMikrotoene.ly:65:23:
> error: not a note name: ch
> Music = \relative c' {
>                      ch2 cl }
> /home/stefan/partituren/vorlagen/snippet_stefansMikrotoene.ly:65:27:
> error: not a note name: cl
> Music = \relative c' {ch2
>                          cl }
>
Does someone know how I can get it  working?
Here is my file:
%%%%%%%%%%%%% SNIPPET
\version "2.20.0"
% Define tunings:
\paper{
#(define fonts (make-pango-font-tree "Century Schoolbook L"
                                      "HE"
                                      "Bitstream Vera Sans Mono"
                         1))
}

#(define-public SyntoHigherNatural 1/12)
#(define-public SyntoLowerNatural -1/12)

StefansPitchnames = #'(
     (ch . ,(ly:make-pitch -1 0 SyntoHigherNatural))
      (cl . ,(ly:make-pitch -1 0 SyntoLowerNatural))
)

pitchnames = \StefansPitchnames
#(ly:parser-set-note-names pitchnames)
FONTNAME = "HE"
SyntoHigherNatural = "o"
SyntoLowerNatural = "m"

StefansStrings = #`(
        (1/12 . ,SyntoHigherNatural)
        (-1/12 . ,SyntoLowerNatural)
)


#(define (my-Y-extent grob)
  (ly:stencil-extent (ly:text-interface::print grob) Y))

\layout {
  \context {
    \Score

    \override Accidental.stencil = #ly:text-interface::print
    \override Accidental.font-name = #FONTNAME
    \override Accidental.text = #(lambda (grob)
                                   (cdr (assoc (ly:grob-property grob
'alteration)
                                          StefansStrings)))
    \override Accidental.font-size = #-1
    \override Accidental.X-extent = #(lambda (grob)
                                       (ly:stencil-extent
                                         (ly:text-interface::print grob) X))
    \override Accidental.Y-extent = #(ly:make-unpure-pure-container
                                       my-Y-extent
                                       (lambda (grob start end)
(my-Y-extent grob)))

    \override Accidental.horizontal-skylines = #'()
    \override Accidental.vertical-skylines = #'()
  }
}

Music = \relative c' {ch2 cl }
\new Staff \Music
%%%%%%%%%%%%%%%% SNIPPET END