Symmetry limit properties of a priori mixing amplitudes for non-leptonic and weak radiative decays of hyperons

We show that, even if a priori mixings of positive-parity but flavour-viola ting eigenstates are allowed in physical hadrons, in the strong flavour sym metry limit the mixing angle will drop out of the matrix elements of the Yu kawa and electromagnetic Hamiltonians that lead to non-leptonic and weak ra diative decays of hyperons in this scheme. We compare this result with rela ted theorems for the same W-mediated decays and give a concrete example of this behaviour by considering the U-spin symmetry of baryons and the U-doub let formed by p and Sigma(+).