Robuta

https://www.mathnet.ru/php/archive.phtml?wshow=paper_refs&WHATTOSHOW=FORWARDLINKS&jrnid=isu&paperid=497&option_lang=eng&wshow=paper M. G. Pleshakov, S. V. Tyshkevich, “One counterexample of shape-preserving approximation”, Izv.... m g s v pleshakov tyshkevich counterexample