A CHORD AS A GROUP OF MODULATION-VARIATIONS OF MELODIC THEMES OVER THE CHORD.
The elements of the group are modulations-variations, and the generators of the group are defined by the intervals of the chord. The exact definition of the variation of a chord-fitting melodic theme is such that it holds group closure to the operation of composition of variations. E.g. idempotent a^2=1, where repeating a shift by an interval is with its complementary interval .
The most relevant layers of the melody is the 1st layer of simplicial submelody, and the 2nd layer of the arpeggios over the chord.
The part of a poetic measure corresponding to a chord, is of course a guide too.
