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Any functor from the category of C*-algebras to the category of locales that assigns to each commutative C*-algebra its Gelfand spectrum must be trivial on algebras of $n$-by-$n$ matrices for $n \geq 3$. This obstruction also applies to other spectra such as those named after Zariski, Stone, and Pierce. We extend these no-go results to functors with values in (ringed) topological spaces, (ringed) toposes, schemes, and quantales. The possibility of spectra in other categories is discussed.
@article{TAC_2014_29_a16, author = {Benno van den Berg and Chris Heunen}, title = {Extending obstructions to noncommutative functorial spectra}, journal = {Theory and applications of categories}, pages = {457--474}, publisher = {mathdoc}, volume = {29}, year = {2014}, language = {en}, url = {http://geodesic.mathdoc.fr/item/TAC_2014_29_a16/} }
Benno van den Berg; Chris Heunen. Extending obstructions to noncommutative functorial spectra. Theory and applications of categories, Tome 29 (2014), pp. 457-474. http://geodesic.mathdoc.fr/item/TAC_2014_29_a16/