  We derive the absolutely anticommuting (anti-)dual-BRST symmetry
transformations for the appropriate Lagrangian densities of the (3 +
1)-dimensional (4D) free Abelian 2-form gauge theory, under which, the total
gauge-fixing term remains invariant. These symmetry transformations are the
analogue of the co-exterior derivative of differential geometry, in the same
sense, as the absolutely anticommuting (anti-)BRST symmetry transformations are
the analogue of the exterior derivative. A bosonic symmetry transformation is
shown to be the analogue of the Laplacian operator. The algebraic structures of
these symmetry transformations are derived and they are demonstrated to be the
reminiscent of the algebra obeyed by the de Rham cohomological operators of
differential geometry.
