lilypond-learning: Simultaneous music expressions multiple staves

 
 Simultaneous music expressions: multiple staves
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 Music Glossary: See(music-glossary)polyphony.
 
    This technique is useful for polyphonic music.  To enter music with
 more voices or more staves, we combine expressions in parallel.  To
 indicate that two voices should play at the same time, simply enter a
 simultaneous combination of music expressions.  A ‘simultaneous’ music
 expression is formed by enclosing expressions inside ‘<<’ and ‘>>’.  In
 the following example, three sequences (all containing two separate
 notes) are combined simultaneously:
 
      \relative c'' {
        <<
          { a2 g }
          { f2 e }
          { d2 b }
        >>
      }
      [image src="" alt="[image of music]" text="image of music"]
 
    Note that we have indented each level of the input with a different
 amount of space.  LilyPond does not care how much (or little) space
 there is at the beginning of a line, but indenting LilyPond code like
 this makes it much easier for humans to read.
 
           Note: each note is relative to the previous note in the input,
           only the first is relative to the ‘c''’ in the initial
           ‘\relative’ command.