GNU LilyPond program usage: 3.4 Updating files with convert-ly

## 3.4 Updating files with `convert-ly`

The LilyPond input syntax is routinely changed to simplify it or improve it in different ways. As a side effect of this, the LilyPond interpreter often is no longer compatible with older input files. To remedy this, the program `convert-ly` can be used to deal with most of the syntax changes between LilyPond versions.

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#### Application Usage