 A mathematical treatment of harmonics informed by Pythagorean principles is also given in the Sectio Canonis, a treatise of debated authorship, but often attributed to Euclid. Nicomachus (fl. c. 100 CE) wrote an influential introduction to harmonics from the Pythagorean standpoint (source texts with commentary are collected in Barker 1990; Barker 2007 reconstructs the development of Pythagorean harmonics.)