TODO.md in head_music-0.22.0 vs TODO.md in head_music-0.23.0

@@ -1,18 +1,113 @@
 # TODO
 
+Disambiguate PitchSet and Sonority
+
+Sonority should be a name for a specific set of intervals
+Sonority.get(identifier)
+Sonority.for(pitch_set)
+Sonority.pitch_set_for(root_pitch:, inversion:)
+
+    class PitchSet
+      def sonority
+        @sonority ||= Sonority.for(self)
+      end
+    end
+
+
+
+open consonance (P5 P8)
+soft consonance (m3 M3 m6 M6)
+mild dissonance (M2 m7)
+sharp dissonance (m2 M7)
+
+P4 (consonant or dissonant)
+T (neutral or restless)
+
+Sets
+DurationSet?
+
+
+Make new analysis classes:
+Dyad
+  .interval
+  .implied_triad (if a third)
+  .possible_triads
+    - returns major and minor if a perfect fifth
+    - returns minor and diminished if minor third
+    - returns major and augmented if major third
+    - returns augmented if augmented fifth
+    - returns diminished if diminished fifth
+    - should it take into account enharmonics? I think yes.
+  .possible_seventh_chords
+    - as above, with either seventh added
+    - returns 3rd inversion if second
+  .possible_chords
+    possible_triads + possible_seventh_chords
+  .possible_enharmonic_triads
+  .possible_enharmonic_seventh_chords
+  .possible_enharmonic_chords
+
+the dyad will be super helpful in analyzing two-part counterpoint.
+
+Triad
+SeventhChord
+Don't need anything beyond seventh chords to analyze pre-Romantic music.
+
+
 ## User stories
 
+
 ### Done
 
     As a developer
+    When instantiating a DiatonicInterval
+    When passing an abbreviation, such as 'P5' or 'm2'
+    I want to receive that instance.
+
+    As a developer
     Given a pitch
-    I want to be able to add a functional interval to get another pitch.
+    I want to be able to add a diatonic interval to get another pitch.
 
-FunctionalInterval
+DiatonicInterval
   - def above(pitch) -> pitch
-FunctionalInterval
+DiatonicInterval
   - def below(pitch) -> pitch
 
 Pitch addition and subtraction
   - define `Pitch#+`, `Pitch#-`
-  - use FunctionalInterval methods
+  - use DiatonicInterval methods
+
+PitchSet
+
+A PitchSet is unlike a PitchClassSet in that the pitches have spellings with octaves rather than Spellings only or octave-less 0-11 designations.
+
+PitchClassSet
+.size?
+.monad?
+.dyad?
+.triad? (must be stacked thirds to be a 'triad')
+.trichord? (all 3-pitch sets)
+
+Should every group of pitches have one or more strategies for describing it? Such as Dyad?
+
+Set (superclass?)
+PitchSet
+  EmptySet
+  Monad
+  Dyad
+  Trichord (or Triad)
+    - triad?
+  Tetrachord (or Tetrad)
+    - seventh_chord?
+  Pentachord (or Pentad)
+  Hexachord (or Hexad)
+  Heptachords (or Heptad or, sometimes, mixing Latin and Greek roots, "Septachord")
+  Octachords (Octad)
+  Nonachords (Nonad)
+  Decachords (Decad)
+  Undecachords
+  Dodecachord
+
+PitchClassSet
+  .normal_form? (most compact)
+  .prime_form (most compact normal form of the original or any inversion)