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Everywhere-regularity for some quasilinear systems with a lack of ellipticity. (English) Zbl 0538.35034

The author proves the \(C^{1,\alpha}\)-everywhere-regularity of the solutions of quasilinear systems having a similar structure as \(div\{| \nabla u|^{p-2}\nabla u\}=f (1<p<\infty)\). He generalizes results due to K. Uhlenbeck [Acta Math. 138, 219-240 (1977; Zbl 0372.35030)] and P.-A. Ivert [Manuscr. Math. 30, 53-88 (1979; Zbl 0429.35033)]. After a differentiation, the above system is not of diagonal form. Nevertheless, K. Uhlenbeck showed that \(| \nabla u|\) satisfies an inequality similar to \(-\Delta | \nabla u|^ 2+\lambda | \nabla^ 2u|^ 2\leq 0 (\lambda>0)\). With the aid of such an inequality, she established a strong maximum principle for \(\nabla u\) which is the key to the everywhere-regularity. The author gives another rather simple proof of that and he treats more general systems than in the article loc. cit.
Reviewer: J.Frehse

MSC:

35J60 Nonlinear elliptic equations
35B45 A priori estimates in context of PDEs
35B50 Maximum principles in context of PDEs
Full Text: DOI

References:

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