FERMIONS
?anti = [Xa(r1)*Xb(r2) - Xb(r1)*Xa(r2) ]* T(t)
Those particles that work with the anti-symmetric wavefunction are called FERMIONS. All of these particles have half-integer spin. Note that if electron 1 and electron 2 both have the same state, ? = 0. This means that both particles can NOT be in the same state at the same location at the same time.