  We review the recent experimental evidence on arbitrary values of the speed
of light within physical media (interior dynamical problems); we recall that
classical (operator) theories with speeds of light different than that in
vacuum are noncanonically (nonunitarily) related to the special relativity,
thus losing the original invariant character with consequential rather serious
problems of physical consistency; we show that the isominkowskian geometry, the
isopoincar\'e symmetry and the isospecial relativity provide a formulation of
arbitrary speeds of light within physical media as invariant as that of the
special relativity for the propagation of light in vacuum; we prove that the
isospecial relativity is directly universal, in the sense of holding for all
possible spacetime models with a symmetric metric directly in the frame of the
observer; we outline the broader genotopic and hyperstructural formulations
which are directly universal for single- and multiple-valued irreversible
systems, respectively, with a generally nonsymmetric metric; we review the
anti-isomorphic isodual formulations for the classical and operator
representation of antimatter and the prediction of the new "isodual photon"; we
finally point out a few representative connections between the invariant
isotopic formulations and a rather large variety of generalized theories
existing in the literature.
