Added basics of Banach algebras.

src/op/notation.tex

@@ -5,4 +5,10 @@
     \textbf{Notation} & \textbf{Description} & \textbf{Source} \\
     \hline
     $1$ & Identity element of a unital algebra. & \autoref{definition:unital-banach-algebra} \\
+    $G(A)$ & Invertible group of a unital algebra. & \autoref{definition:banach-algebra-invertible} \\
+    $G_0(A)$ & The identity component of $G(A)$. & \autoref{definition:identity-component} \\
+    $I(A)$ & The index group of $A$. & \autoref{definition:index-group} \\
+    $\sigma_A(x) = \sigma(x)$ & The spectrum of $x$ in $A$. & \autoref{definition:spectrum} \\
+    $R_x(\lambda)$ & The resolvent of $x$. & \autoref{definition:resolvent} \\ 
+    $[x]_{sp}$ The spectral radius of $x$. & \autoref{definition:spectral-radius}
 \end{tabular}