Hello,
Each movement of a piano piece has a separate file. In each movement the various voices are identified by a variable, e.g., ArightOne, BleftTwo. Each file compiles perfectly individually. When the file is copied into \bookpart { \header { } Copied here } It does not compile correctly and the error: syntax error, unexpected SYMBOL appears repeatedly followed by one of the variable names, e.g. ArightOne = \relative c'' { What is my error? Thank you for your kind attention. Mark