// This cd should be modified not to use syntax between optional part.
// The problem in such a case is, which edge do you assign the syntax to?
// If you want syntax there, introduce an extra class.

Example = Tree.
Tree ="(" <l> Label
  [<left> Tree] "."
  [<right> Tree] ")".
Label = <v> int.

Main = .

*visitors*
SummingVisitor = <total> int.
SummingVisitor2 = <total> int.