  The WDVV equations of associativity in 2-d topological field theory are
completely integrable third order Monge-Amp\`ere equations which admit
bi-Hamiltonian structure. The time variable plays a distinguished role in the
discussion of Hamiltonian structure whereas in the theory of WDVV equations
none of the independent variables merits such a distinction. WDVV equations
admit very different alternative Hamiltonian structures under different
possible choices of the time variable but all these various Hamiltonian
formulations can be brought together in the framework of the covariant theory
of symplectic structure. They can be identified as different components of the
covariant Witten-Zuckerman symplectic 2-form current density where a
variational formulation of the WDVV equation that leads to the Hamiltonian
operator through the Dirac bracket is available.
