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\begin{equation*}
\cal{C}:= \mbox{span}\{\otimes_{i=1}^N |\alpha_i\rangle_i\,/\, \alpha_i=0,1\}\cong ({{\rm\kern.24em \vrule width.04em height1.46ex depth-.07ex
\kern-.30em C}}^2)^{\otimes\,N}.
\end{equation*}
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