Hi. I write :

Code:

\begin{tikzpicture}[auto,>=stealth']
\node (L) {$\frac{L}{Z(L)}\times \frac{L}{Z(L)}$};
\node[right=of L] (L1) {${L}^2$};
\node[below=of L] (M) {$\frac{M}{Z(M)}\times \frac{M}{Z(M)} $};
\node[below=of L1] (M1) {$M^2$};
\draw[->] (L) -- node[swap] {$\alpha \times \alpha$} (M);
\draw[->] (L1) -- node[] {$\beta$} (M1);
\draw[->] (L) -- node {} (L1);
\draw[->] (M) -- node {} (M1);
\path[use as bounding box] (-1.5,0) rectangle (0,0);
\end{tikzpicture}

but in pdf the arrows was tilted. What I do for this problem?

thanks