      \fitem{make_label_pitches}() \emph{or} (start:numeric) \emph{or}
      (start:numeric, stop:numeric): %%
      returns a map associating a vector of pitches to the label of an
      event. A \code{NOTE} corresponds to a tab of size 1, a
      \code{CHORDS} with $n$ pitches to a tab of size $n$, \emph{etc.}.
      Events with no label do not appear in the map.
      %% 
      Called with no arguments, the events considered are all
      the events in the score. With \code{start}, only the events whose
      position is greater than \code{start} are considered. If a
      \code{stop} is specified, all events must have a position between
      \code{start} and \code{stop}.

      %%% -------------------------------------------------------

