OPTIC: + cardinality - doublings removed: the set class's prime form
Number of distinct pitch classes
OPTI: + inversion - the more compact of T and its inversion's T
O: octave equivalence - pitch classes in voice order, doublings kept
OP: + permutation - pitch classes sorted, doublings kept
OPT: + transposition - the most compact rotation (normal form), starting on 0
A chord under the OPTIC equivalences, each one added to the previous (O, OP, OPT, OPTI, OPTIC), in 12-TET pitch classes.