Andrew M. Baxter, Ronald Umble. Periodic Orbits for Billiards on an Equilateral Triangle. The American Mathematical Monthly, 115(6):479-491, 2008. [doi]
@article{BaxterU08,
title = {Periodic Orbits for Billiards on an Equilateral Triangle},
author = {Andrew M. Baxter and Ronald Umble},
year = {2008},
url = {http://www.jstor.org/stable/27642528},
researchr = {https://researchr.org/publication/BaxterU08},
cites = {0},
citedby = {0},
journal = {The American Mathematical Monthly},
volume = {115},
number = {6},
pages = {479-491},
}