I understand the basics of the pauli exclusion principle emerging from antisymmetric wavefunctions being invalid for two fermions with the same quantum numbers. I've also seen how, empirically, you can add a term to the potential energy, of (e.g.) the ionic bond between K+ and Cl-, that incorporates the effects of an exclusion force preventing the atoms from merging (or coming closer than some optimal distance). How can one transition from a wavefunction simply not being allowed, to the existence of a new potential energy term (and therein force)? Some moderately-rigorous mathematics might help. Similarly, how do you derive something like the degeneracy pressure in a neutron star from the pauli exclusion principle? Thanks!