\Bibitem{GusFed89} \by V.~R.~Gushchin, A.~V.~Fedorov \paper Asymptotic analysis of inviscid perturbations in a supersonic boundary layer \jour Prikl. Mekh. Tekh. Fiz. \yr 1989 \vol 30 \issue 1 \pages 69--75 \mathnet{http://mi.mathnet.ru/pmtf4557} \transl \jour J. Appl. Mech. Tech. Phys. \yr 1989 \vol 30 \issue 1 \pages 64--70 \crossref{https://doi.org/10.1007/BF00860706}