A Free Group of Rotations of Rank 2

Abstract

One of the key steps in the proof of the Banach-Tarski Theorem is the introduction of a free group of rotations. First, a free group of reduced words is generated where each element of the set is represented as an ACL2 list. Then we demonstrate that there is a one-to-one relation between the set of reduced words and a set of 3D rotations. In this paper we present a way to generate this set of reduced words and we prove group properties for this set. Then, we show a way to generate a set of 3D matrices using the set of reduced words. Finally we show a formalization of 3D rotations and prove that every element of the 3D matrices set is a rotation.

In Proceedings ACL2 2022, arXiv:2205.11103