Material equations and Maxwell's equations for isotropic media; waves with negative group velocity and negative values of $\varepsilon$($\omega$) and $\mu(\omega)$

The frequently used Maxwell's equations that contain E, B, D, and H fields are only substantiated in the framework of linear material equations and for isotropic media alone. We have shown that accounting for the deviation of magnetic permittivity $\mu (\omega )$ from unity in the usually employed dispersion equation implies a false precision. Therefore, if spatial dispersion is disregarded, transverse waves only exist in the energy region where $\varepsilon (\omega)$>0 and have a positive group velocity.