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@article{DE_1977_13_2_a1, author = {N. P. Erugin}, title = {The {Riemann} problem. {III.~The} case $n=2$ and $m=4$}, journal = {Differencialʹnye uravneni\^a}, pages = {238--254}, publisher = {mathdoc}, volume = {13}, number = {2}, year = {1977}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DE_1977_13_2_a1/} }
N. P. Erugin. The Riemann problem. III.~The case $n=2$ and $m=4$. Differencialʹnye uravneniâ, Tome 13 (1977) no. 2, pp. 238-254. http://geodesic.mathdoc.fr/item/DE_1977_13_2_a1/