From the introduction: "The tone sandhi of Peñoles Mixtec is accounted for by a small number of simple, interrelated rules, involving the two tones high and low and the modification or lack of modification of these tones in specified environments. The tones high and low are formally represented by the feature [high] in its two values plus and minus, and the modification or lack of modification of them by the feature [modify] in its two values. The two tonal features have their values changed by the tone rules, in environments specified phonologically and to a limited extent, syntactically.
"In this paper we will consider the four rules which account for tone sandhi in sequences consisting solely of bisyllabic morphemes, inasmuch as the most important aspects of tone sandhi are manifested in these sequences. We will also consider the order in which the rules must apply, the need for the tone cycle, and the way in which the tone cycle reduces the number of ordering restrictions."
Daly, John P.
"Tone sandhi and rule ordering in Peñoles Mixtec,"
Work Papers of the Summer Institute of Linguistics, University of North Dakota Session: Vol. 17, Article 4.
Available at: https://commons.und.edu/sil-work-papers/vol17/iss1/4