Neil tried to simplify an expression step by step.
$\begin{align}
&\dfrac{5^{-6}} {5^{-4}}
\\\\
=&5^{-6-(-4)}&\green{\text{Step } 1}
\\\\
=&5^{-2}&\blue{\text{Step } 2}
\\\\
=&\dfrac{1}{5^2}&\purple{\text{Step } 3}
\end{align}$
**Find Neil's mistake.**
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