Strong anomaly and ??3p decay

The amplitude for eta ..-->.. 3..pi.. is calculated in terms of the amplitude for eta' ..-->.. eta..pi pi.. using the strong anomaly and the partial conservation of the U(1) current. The isospin violation, an (m/sub u/-m/sub d/)/(m/sub u/+m/sub d/) effect, is large. The eta' decay constant is estimated from psi ..-->.. eta'..gamma... The result for eta ..-->.. 3..pi.. is in good agreement with experiment.