constraint surface ⌺. On the extended phase space N constructed in the BFV quantization, we can consider the dynamical system whose constraint surface, by definition, is Z Q ͑in local coordinates on N, the constraints can be chosen as the components of Q͒. Then the constrained systems (N 0 ,⌺) and (N,Z Q ) are equivalent: the respective algebras of the equivalence classes of observables are naturally isomorphic as Poisson algebras.Beyond the BRST context, algebras of functions on QP manifolds, which are differential Poisson algebras ͑associative supercommutative algebras endowed with a bracket operation and a differential that is a derivation of the bracket͒ can arise from complexes endowed with a supercommutative associative multiplication and a Gerstenhaber-like multiplication ͑''bracket''͒; the differential is then interpreted as the Q structure, and the bracket becomes the P structure ͓the Poisson or the BV bracket on the dual ͑super͒manifold͔. The basic examples are the cohomology complexes of a Lie algebra a with coefficients in ٙa or Sa ͑the exterior and symmetric tensor algebras͒; the general case involves L ϱ algebras. 8 In this algebraic context, reduction to the zero locus can yield relations between different complexes. In certain cases, the zero-locus reduction can be applied repeatedly; the equation ensuring the existence of a nilpotent vector field on the reduced manifold at the second step of the reduction can be the classical Yang-Baxter equation ͑CYBE͒, in which case the reduction leads to the well-known Sklyanin and Berezin-Kirillov brackets.In addition to the usual QP manifolds, one can consider bi-QP manifolds, which are the geometric counterparts of bicomplexes, and in physical terms, originate in the BRST-anti-BRST ͓Sp͑2͒-symmetric/triplectic͔ quantization. 9-12 With two BRST operators represented by two commuting ͑odd and nilpotent͒ vector fields, bi-QP manifolds might be called QQP manifolds; interestingly enough, the corresponding zero-locus reduction ͑to the submanifold on which both vector fields vanish͒ results in a ''PP'' manifold, i.e., gives rise to a bi-Hamiltonian structure. A typical example is obtained by starting with a Lie algebra a and deriving the second differential from a coalgebra structure. Compatibility between two differentials then implies that (a,a*,a a*) is a Manin triple. 13 There also exists an alternative construction of a bi-QP manifold from a single Lie algebra structure, which results in non-Abelian triplectic antibrackets 14 on the space of common zeroes of the differentials ͑and thus, the zero locus reduction leads to a nontrivial relation to the bicomplex used in the extended BRST symmetry͒. This paper is organized as follows. In Sec. 2.2, we recall the main points of the zero locus reduction on ͑odd or even͒ QP manifolds. Symmetries of QP manifolds are reviewed in Sec. 2.3. In Sec. 3, we turn to a more detailed analysis of even QP manifolds corresponding to the BFV quantization. In Secs. 3.1-3.2, we recall several facts about the BFV formalism in the form...