The maximum principle 2026-02-15T22:53:38+03:00 DEBUG: VuFind\ILS\Driver\Folio: Token taken from global cache: eyJhbGciOiJIUzI1NiJ9.eyJzdWIiO... - Pucci, Patrizia; Serrin, J. (James), 1926- (Progress in nonlinear differential equations and their applications ;, 2007)