+ Drul_array<bool> add_point (Pitch);
+ bool is_empty () const;
+};
+
+class Pitch_lexicographic_interval : public Drul_array<Pitch>
+{
+public:
+ Pitch_lexicographic_interval ();
+ Pitch_lexicographic_interval (Pitch, Pitch);
+ Drul_array<bool> add_point (Pitch);