Minor edits

Advanced/Mock a Mockingbird/parts/01 tmam.tex

@@ -164,7 +164,7 @@ Show that any bird that is fond of at least one bird is compatible with itself.
 \begin{solution}
 	\begin{alltt}
 		let A
-		let x so that Ax := x
+		let x so that Ax = x
 		Ax = x  \qed{}
 	\end{alltt}
 	That's it.