\Bibitem{San62} \by V.~Yu.~Sandberg \paper Lipschitz spaces \jour Dokl. Akad. Nauk SSSR \yr 1962 \vol 145 \issue 2 \pages 284--286 \mathnet{http://mi.mathnet.ru/dan26726} \mathscinet{https://mathscinet.ams.org/mathscinet-getitem?mr=0144296} \zmath{https://zbmath.org/?q=an:0128.40901}