[tex]
\begin{cases}
BT\approx EU \\
BU\approx ET
\end{cases}
[/tex]
If [tex]B\approx E[/tex] then
BT\approx BU \\
BU\approx BT
Or simply
[tex]BU\approx BT[/tex]
Since [tex]BU\approx BT[/tex] we obtain that [tex]U\approx T[/tex] hence [tex]B\approx E[/tex] must apply for the aproximity to stand.
Hope this helps.
