\begin{align}
  f(x)=
  \begin{cases}
    -x^2,  &\text{if $x \textless 0 $; } \\
    \alpha + x,    &\text{otherwise.}
  \end{cases}
\end{align}


\subseteq
\subsetneq
\subsetneqq


\noindent This is a book. 


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\bibitem{ } Ramakrishnan, Valenza, ``Fourier Analysis on Number Fields",  Springer, 1999.
\bibitem{ } Mumford, ``The Red book of varieties and schemes", Springer-Verlag, 1988.
\bibitem{ } Neal Koblitz, ``P-adic numbers, p-adic analysis, and zeta-functions",  Springer-Verlag, 1977.
\bibitem{ } Platonov, ``Algebraic groups and number theory",  Boston Academic Press , 1994.
\end{thebibliography}

\begin{thebibliography}{100} 
\bibitem{ } .
\end{thebibliography}