“…The proof requires only a slight modification from that of Buchholz and Epstein. Namely, the role of the square of the Pauli-Lubanski vector as a Casimir operator is, in 2+1 dimensions, played by a scalar operator, the so-called Pauli-Lubanski scalar [1,13] which is defined as follows. Let U be a representation of the universal covering of the Poincaré group in three spacetime dimmensions, let L 0 denote the generator of the rotation subgroup in the representation U , and let L i be the generator of the boosts in direction…”