  The usual formulation of time-dependent mechanics implies a given splitting
$Y=R\times M$ of an event space $Y$. This splitting, however, is broken by any
time-dependent transformation, including transformations between inertial
frames. The goal is the frame-covariant formulation of time-dependent mechanics
on a bundle $Y\to R$ whose fibration $Y\to M$ is not fixed. Its phase space is
the vertical cotangent bundle $V^*Y$ provided with the canonical 3-form and the
corresponding canonical Poisson structure. An event space of relativistic
mechanics is a manifold $Y$ whose fibration $Y\to R$ is not fixed.
