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## Le carnet de Rufus Bowen

Rufus Bowen, mort en 1975 à l’âge de 31 ans, a laissé un carnet contenant 157 problèmes mathématiques. A l’occasion de la conférence “Rufus Bowen”, Brian Marcus a organisé sa publication commentée sur un site web permettant à chacun de le feuilleter et surtout de contribuer.

Duncan SANDS gave a talk for the Journée Affine Par Morceaux on the dynamics of Lozi maps. These are the piecewise affine homeomorphisms of the plane of the form $(x,y)\mapsto(1-a|x|+by,x)$ where $ab\ne0$. Lozi introduced them as a toy model for the Hénon map, observing numerically some kind of strange attractor for $(a,b)=(1.7,0.5)$. SANDS and ISHII have especially studied their topological entropy. The following picture shows what is known and what is not in the parameter plane:
In the grey area the entropy is known to be zero. In the turquoise area it is known to be positive (and maximal, ie, log 2, in the hatched part). In the white area in-between, there are examples with positive entropy (on $b=-1$ for the part below the axis) but otherwise little is known.