  In the usual description of electrons in metals and superconductors, the
single electron states are assumed to satisfy Bloch's theorem. This is because
the electron-ion interaction is privileged over the electron-electron
interaction. However the theory of hole superconductivity proposes that in the
transition to superconductivity carriers `undress' from the electron-ion
interaction. I propose here a new basis set to describe electrons in the
superconducting state that does not satisfy Bloch's theorem but instead is
designed to optimize the electron-electron interaction. The new basis set
favors a superconducting state where a spin current exists and where states
near the bottom of the band become partially occupied, as predicted by the
theory of hole superconductivity.
