  We unify the Lorentz- and O(2) duality-covariant approach to 4D self-dual
theories by Pasti, Sorokin and Tonin (PST) with the formulation involving an
auxiliary tensor field. We present the basic features of the new hybrid
approach, including symmetries of the relevant generalized PST action. Its
salient peculiarity is the unique form of the realization of the PST gauge
symmetries. The corresponding transformations do not affect the auxiliary
tensor field, which guarantees the self-duality of the nonlinear actions in
which the O(2) invariant interactions are constructed out of the tensor field.
