2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/226878The Pauli exclusion principle can be stated as inequality $<ψ|ρ|ψ>\le 1$ for the electron density matrix $ρ$. Nowadays it is replaced by skew symmetry of the multi-electron wave function. The replacement leads to numerous additional constraints on $ρ$, which are discussed in this letter together with their physical implications, in particular for spin magnetic moment of a multi-electron system.Submitted to Phys. Rev. Letters, 4 pagesQuantum Physicstext