## 5.6 Using music functions

Where tweaks need to be reused with different music expressions, it is often convenient to make the tweak part of a music function. In this section, we discuss only substitution functions, where the object is to substitute a variable into a piece of LilyPond input code. Other more complex functions are described in Music functions.

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#### LilyPond — Notation Reference v2.18.2 (稳定分支).