\Bibitem{Kny85} \by A.~V.~Knyazev \paper Sharp a priori error estimates of the Rayleigh--Ritz method without assumptions of fixed sign or compactness \jour Mat. Zametki \yr 1985 \vol 38 \issue 6 \pages 900--907 \mathnet{http://mi.mathnet.ru/mzm5603} \mathscinet{http://mathscinet.ams.org/mathscinet-getitem?mr=823428} \zmath{https://zbmath.org/?q=an:0601.65032} \transl \jour Math. Notes \yr 1985 \vol 38 \issue 6 \pages 998--1002 \crossref{https://doi.org/10.1007/BF01157020} \isi{https://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=Publons&SrcAuth=Publons_CEL&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=A1985D419300029}