Pauli Exclusion Principle
?sym = [Xa(r1)*Xb(r2) + Xb(r1)*Xa(r2) ]* T(t)
?anti = [Xa(r1)*Xb(r2) - Xb(r1)*Xa(r2) ]* T(t) .
Which (if either) possibility agrees with experiment?
It turns out that some particles are explained nicely by the symmetric, and some are explained by the antisymmetric.