Finite groups of automorphisms of Enriques surfaces and the Mathieu group $M_{12}$

Shigeru Mukai, Hisanori Ohashi

An action of a group $G$ on an Enriques surface $S$ is called Mathieu if it acts on $H^0(2K_S)$ trivially and every element of order 2, 4 has Lefschetz number 4. A finite group $G$…