The variational principles of mechanics 2026-02-15T23:54:03+03:00 DEBUG: VuFind\ILS\Driver\Folio: Token taken from global cache: eyJhbGciOiJIUzI1NiJ9.eyJzdWIiO... - Lanczos, Cornelius, 1893-1974 (Mathematical expositions ;, 1986)