A new bound on Banach-Mazur distance between planar convex bodies

Serhii Brodiuk, Nazarii Palko, Andriy Prymak

Published 2017-07-16Version 1

We prove that the Banach-Mazur distance between any two planar convex bodies is at most $\tfrac{19-\sqrt{73}}4<2.614$, improving the previously known bound of $3$ obtained by Lassak. For the lower bound, it is known that the Banach-Mazur distance between a regular pentagon and a triangle is $1+\frac{\sqrt{5}}{2}\approx 2.118$.