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\begin{document}


\begin{align} 
A &=0\Longrightarrow0\longrightarrow0+4=4\pmod{\ 26})=4\Longrightarrow 4=E\\
T &=19\Longrightarrow19\longrightarrow19+4=23\pmod{\ 26}=23\Longrightarrow 23=X\\
\end{align}



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