  The three well-known forms of relativistic dynamics are unitarily equivalent
and the problem of constructing the current operators can be solved in any
form. However the notion of the impulse approximation is reasonable only in the
point form. In particular, the parton model which is the consequence of the
impulse approximation in the front form is incompatible with Lorentz
invariance, P invariance and T invariance. The results for deep inelastic
scattering based on the impulse approximation in the point form give natural
qualitative explanation of the fact that the values given by the parton model
sum rules exceed the corresponding experimental quantities.
