New in version 2.0.
List harmonic chromatic intervals in expr:
abjad> staff = Staff("c'8 d'8 e'8 f'8")
abjad> for interval in sorted(pitchtools.list_harmonic_chromatic_intervals_in_expr(staff)):
... interval
...
HarmonicChromaticInterval(1)
HarmonicChromaticInterval(2)
HarmonicChromaticInterval(2)
HarmonicChromaticInterval(3)
HarmonicChromaticInterval(4)
HarmonicChromaticInterval(5)
Return unordered set.