Original sentence: Most Greek theorists distinguish three genera of the tetrachord: enharmonic, chromatic, and diatonic (Barbera 1984, 229)
Edited sentence: Most Greek theorists distinguish three genera of the tetrachord: enharmonic, chromatic, and diatonic.The enharmonic and chromatic genera are defined by the size of their largest incomposite interval (major third and minor third, respectively), which leaves a composite interval of two smaller parts, together referred to as a pyknon; in the diatonic genus, no single interval is larger than the other two combined (Barbera 1984, 229)