Necessary conditions for the Cauchy problem for non-strictly hyperbolic equations to be well-posed. (English. Russian original) Zbl 0312.35049
Russ. Math. Surv. 29, No. 5, 1-70 (1974); translation from Usp. Mat. Nauk 29, No. 5(179), 3-70 (1974).
MSC:
35L30 | Initial value problems for higher-order hyperbolic equations |
35A99 | General topics in partial differential equations |