Since it will be the first spring seminar in 2021 we will try to enjoy
some mathematics related to Euclidean geometry and group theory
considering the question of (non) existence of closed chains composed of
tetrahedra, such that the next tetrahedron is a reflection of the
previous with respect to one of its sides. For other regular polyhedra
closed chains exist. The seminar is a result of random leafing through
Extracta Mathematicae where the title Scottish Book and some
familiar names as prof. Stanisław Janeczko and Hugo Steinhaus caught my
eye. The talk is based on the paper by Ian Steward Tetrahedral chains
and a curious semigroup, Extracta Mathematicae, vol 34, No 1, 2019.