+@cindex multiple staves
+@cindex staves, multiple
+@cindex polyphony
+@cindex combining expressions in parallel
+@cindex parallel expressions
+@cindex expressions, parallel
+@cindex relative notes and simultaneous music
+@cindex relative notes and parallel expressions
+@cindex simultaneous music and relative notes
+@cindex parallel expressions and relative notes
+
+@funindex <<
+@funindex >>
+@funindex << ... >>
+