  Starting from the requirement that a Lagrangian field theory be invariant
under both Schwinger-Dyson BRST and Schwinger-Dyson anti-BRST symmetry, we
derive the BRST--anti-BRST analogue of the Batalin-Vilkovisky formalism. This
is done through standard Lagrangian gauge fixing respecting the extended BRST
symmetry. The solutions of the resulting Master Equation and the gauge-fixing
procedure for the quantum action can be brought into forms that coincide with
those obtained earlier on algebraic grounds by Batalin, Lavrov and Tyutin.
