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• CommentRowNumber1.
• CommentAuthorUrs
• CommentTimeMay 9th 2022

I have added a section (here) highlighting the remarkable result of

that the vacua of the free Dirac field in a static Coulomb background are characterized by Fredholm operators whose kernel/cokernel are the Hilbert subspaces of inhabited electron/positron states in the resulting charged vacuum.

As far as I am aware, this result has not been followed up on (but please drop me a note if you know of developments). At the same time, this is plausibly the result which is needed in order to actually prove the conjectured K-theory classification for topological phases of matter (which, despite common impression, is far from established)