1. N. Alkoumi, F. Schlenk, Shortest closed billiard orbits on convex tables. Manuscripta Math. 147, 365–380 (2015)
2. R. Courant, H. Robbins, What is mathematics? An Elementary Approach to Ideas and Methods, 2nd edn. (Oxford University Press, Oxford, 1996)
3. H.S.M. Coxeter, S.L. Greitzer, Geometry Revisited (AMS, Washington, DC, 1967)
4. V. Cyr, A number theoretic question arising in the geometry of plane curves and in billiard dynamics. Proc. Am. Math. Soc. 140(9), 3035–3040 (2012)
5. H. Dorrie, 100 Great Problems of Elementary Mathematics: Their History and Solutions (Dover, New York, 1963)