  The effective super-renormalizable 3-dimensional Lagrangian, describing the
high temperature limit of chiral gauge theories, has more symmetry than the
original 4d Lagrangian: parity violation is absent. Parity violation appears in
the 3d theory only through higher-dimensional operators. We compute the
coefficients of dominant P-odd operators in the Standard Electroweak theory and
discuss their implications. We also clarify the parametric accuracy obtained
with dimensional reduction.
