  We present a relativistic generalization of the Wigner inequality for the
scalar and pseudoscalar particles decaying to two particles with spin (fermions
and photons.) We consider Wigner's inequality with the full spin
anticorrelation (with the non-relativistic analog) as well as the case with the
full spin correlation. The latter case may be obtained by a special choice of
the plane of measurement of the spin projections on the direction of
propagation of fermions. The possibility for relativistic testing of Bohr's
complementarity principle is shown.
