  Having in mind that physical systems have different levels of structure we
develop the concept of external, internal and total improper Lorentz
transformation (space inversion and time reversal). A particle obtained from
the ordinary one by the application of internal space inversion or time
reversal is generally a different particle. From this point of view the
intrinsic parity of a nuclear particle (`elementary particle') is in fact the
external intrinsic parity, if we take into account the internal structure of a
particle. We show that non-conservation of the external parity does not
necessarily imply non-invariance of nature under space inversion. The
conventional theory of beta-decay can be corrected by including the internal
degrees of freedom to become invariant under total space inversion, though not
under the external one.
