  Exact correspondence between Israel-Stewart theory and first-order causal and
stable hydrodynamics is established for the boost-invariant massive case with
zero baryon density and the same constant relaxation times used in the shear
and bulk sectors. Explicit expressions for the temperature dependent regulators
are given for the case of a relativistic massive gas. The stability and
causality conditions known in the first-order approach are applied and one
finds that one of them is violated in this case.
