TY  - JOUR
AU  - H. Stachel 
TI  - Isometric Billiards in Ellipses and Focal Billiards in Ellipsoids
JO  - Journal for geometry and graphics
PY  - 2021
SP  - 97
EP  - 118
VL  - 25
IS  - 1
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/JGG_2021_25_1_JGG_2021_25_1_a8/
ID  - JGG_2021_25_1_JGG_2021_25_1_a8
ER  -