\documentclass{article}
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\begin{LTR}

$$%
\begin{array}{ccccccccccc}
{\cal M}^{(c)}(L, N) & \rightarrow  & {\cal M}^{(c)}(\frac{L}{A_{n-1}}, \frac{N}{A_{n-1}}) & \rightarrow
& \frac{A_{n-1}}{A_{n}} & \rightarrow  & \frac{N}{\gamma _{c+1}(N, L)} &
\rightarrow  & \frac{N}{\gamma _{c+1}(N, L)+A_{n-1}} & \rightarrow  & 0 \\
\downarrow \alpha _{1} &  & \downarrow \alpha _{2} &  & \downarrow \alpha
_{3} &  & \downarrow \alpha _{4} &  & \downarrow \alpha _{5} &  &  \\
{\cal M}^{(c)}(H, K) & \rightarrow  & {\cal M}^{(c)}(\frac{H}{B_{n-1}}, \frac{K}{B_{n-1}}) & \rightarrow
& \frac{B_{n-1}}{B_{n}} & \rightarrow  & \frac{K}{\gamma _{c+1}(K, H)} &
\rightarrow  & \frac{K}{\gamma _{c+1}(K,H)+B_{n-1}} & \rightarrow  & 0.%
\end{array}%
$$
\end{LTR}
\end{document}