 The first non-spatiotemporal symmetry to be introduced into microphysics, and also the first symmetry to be treated with the techniques of group theory in the context of quantum mechanics, was permutation symmetry (or invariance under the transformations of the permutation group). This symmetry, “discovered” by W. Heisenberg in 1926 in relation to the indistinguishability of the “identical” electrons of an atomic  system,[12]  is the discrete symmetry (i.e. based upon groups with a discrete set of elements) at the core of the so-called quantum statistics (the Bose-Einstein and Fermi-Dirac statistics), governing the statistical behaviour of ensembles of certain types of indistinguishable quantum particles (e.g. bosons and fermions). The permutation symmetry principle states that if such an ensemble is invariant under a permutation of its constituent particles then one doesn’t count those permutations which merely exchange indistinguishable particles, that is the exchanged state is identified with the original state (see French and Rickles, 2003, Section 1).