"... was formalized by a number of authors ... as the requirement that the wave function of a multi-electron system is in the coordinates, and , of all the electrons. This principle was incorporated into statistical mechanics by Enrico Fermi ... and Dirac, ... and for this reason particles obeying the exclusion principle are generally called 's,' just as particles like photons for which the wave function is symmetric and which obey the statistics of Bose and Einstein are called 's.'"