2020/02/23 by Fierobe, Corentin
#Dynamical Systems (math.DS) #FOS: Mathematics
paper · doi:10.48550/arxiv.2002.09845
In the class of projective billiards, which contains the usual billiards, we exhibit counter-examples to Ivrii's conjecture, which states that in any planar billiard with smooth boundary the set of periodic orbits has zero measure. The counter-examples are polygons admitting a 2-parameters family of n-periodic orbits, with n being either 3 or any even number grower than 4.