Upgraded prose.

src/op/banach/multiplicative.tex

@@ -97,12 +97,12 @@
         &= 2[x(yxy) + y(xyx)] \in \ker \phi
     \end{align*}
 
-    and $(xy - yx)^2 \in \ker\phi$ as well, and
+    and $(xy - yx)^2 \in \ker\phi$. Since
     \[
     (\phi(xy - yx))^2 = \phi((xy - yx)^2) = 0
     \]
 
-    Therefore $2xy = (xy + yx) - (xy - yx) \in \ker \phi$, $\ker \phi$ is an ideal, and $\phi$ is a homomorphism. 
+    The commutator $xy - yx \in \ker \phi$ as well. Therefore $2xy = (xy + yx) - (xy - yx) \in \ker \phi$, $\ker \phi$ is an ideal, and $\phi$ is a homomorphism. 
 \end{proof}