### 2.20 An orchestral part

In orchestral music, all notes are printed twice: both in a part for the musicians, and in a full score for the conductor. Identifiers can be used to avoid double work: the music is entered once, and stored in a variable. The contents of that variable is then used to generate both the part and the score.

It is convenient to define the notes in a special file, for example, suppose that the horn-music.ly contains the following part of a horn/bassoon duo,

         hornNotes = \notes \relative c {
           \time 2/4
           r4 f8 a cis4 f e d
         }

Then, an individual part is made by putting the following in a file

         \include "horn-music.ly"
         \header {
           instrument = "Horn in F"
         }
         \score {
           \notes \transpose f c' \hornNotes
         }

The line

           \include "horn-music.ly"

substitutes the contents of horn-music.ly at this position in the file, so `hornNotes` is defined afterwards. The command `\transpose f c'` indicates that the argument, being `\hornNotes`, should be transposed by a fifth downwards: sounding `f` is denoted by notated `c'`, which corresponds with tuning of a normal French Horn in F. The transposition can be seen in the following output

In ensemble pieces, one of the voices often does not play for many measures. This is denoted by a special rest, the multi-measure rest. It is entered with a capital `R` followed by a duration (1 for a whole note, 2 for a half note, etc.) By multiplying the duration, longer rests can be constructed. For example, this rest takes 3 measures in 2/4 time

         R2*3

When printing the part, multi-rests must be condensed. This is done by setting a run-time variable

         \set Score.skipBars = ##t

This commands sets the property `skipBars` property in the `Score` context to true (`##t`). Prepending the rest and this option to the music above, leads to the following result

The score is made by combining all of the music in a `\score` block. Assuming that the other voice is in `bassoonNotes` in the file bassoon-music.ly, a score is made with

         \include "bassoon-music.ly"
         \include "horn-music.ly"

         \score {
           \simultaneous {
             \new Staff \hornNotes
             \new Staff \bassoonNotes
           }
         }

leading to

More in-depth information on preparing parts and scores in the notation manual, in Orchestral music.

Setting run-time variables (“properties”) is discussed in ref-TODO.

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