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.