@article{1103044465, author = {Ludford, G. S. S.}, title = {Generalised Riemann invariants.}, journal = {Pacific J. Math.}, volume = {5}, number = {4}, year = {1955}, pages = { 441-450}, language = {en}, url = {http://dml.mathdoc.fr/item/1103044465} }
Ludford, G. S. S. Generalised Riemann invariants.. Pacific J. Math., Tome 5 (1955) no. 4, pp. 441-450. http://gdmltest.u-ga.fr/item/1103044465/