\subsection{Notation}
-A surreal number $X$ consisting of left set $X_L$ and right set $X_R$ is
+A surreal number $x$ consisting of left set $X_L$ and right set $X_R$ is
represented as \surreal{X_L}{X_R}. The void set, as Knuth named it, is
represented by leaving the appropriate left or right set empty, as in
\surreal{}{}, the first surreal number defined.