Added basics of C*-algebras.

src/op/c-star/order.tex

@@ -0,0 +1,10 @@
+\section{Order Structures of $C^*$-Algebras}
+\label{section:order-c-star-algebra}
+
+\begin{definition}[Positive]
+\label{definition:positive-c-star-algebra}
+    Let $A$ be a $C^*$-algebra and $x \in A$, then $x$ is \textbf{positive} if there exists $y \in A$ such that $x = y^*y$. 
+\end{definition}
+
+
+