\documentclass[12pt]{article}
\usepackage{amsmath,amssymb,amsfonts}
\begin{document}
In this paper, we determine derivations of affine Lie superalgebras. As the nature of affine Lie superalgebra of type $A(\ell,\ell)^{(1)}$ is slightly different from the nature of the other types; we study separately the derivations for type $X= A(\ell,\ell)^{(1)}$ and $X\neq A(\ell,\ell)^{(1)}.$ We precisely determine derivations up to inner derivations; in the former type, we get a 4-dimensional vector space while in the latter one, we get a 1-dimensional vector space.
\end{document}