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\begin{document}
\[ \]
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\begin{flalign}
D^{\alpha}_{x}x^{\gamma}=\frac{\Gamma(\gamma+1)}{\Gamma(\gamma+1-\alpha)}\:x^{\gamma-\alpha} 
\end{flalign}

\begin{equation}
P\left( u,\:D^{\alpha}_{t}u, u_{x},D^{2\alpha}_{t}u, u_{xx},\ldots\right)=0 	
\end{equation}

\end{document}