Automorphisms of Twisted Chevalley Groups of type ${}^2{A}_{\mathrm{\ell }}(\mathrm{\ell }\ge 5)$ over Local Rings

This paper is the first in a series devoted to the classification of automorphisms and isomorphisms of twisted Chevalley groups over commutative rings. In the present paper, we prove that every automorphism of a twisted Chevalley group of type ${}^2{A}_{\mathrm{\ell }}$ $(\mathrm{\ell }\ge 5)$ over a local ring in which $2$ is invertible is standard.