This is to me the best explanation so far of the Russian negotating strategy in the Trump-Putin-conversations on a ceasefire in Ukraine. https://www.youtube.com/watch?v=GvXkuurLupY (after 2:15). English subtitles available.

(Christoph Wanner is a correspondet of the conservative German news outlet Welt. But he studied (perhaps even majored in) law and Slavonic studies before becoming a correspondent in Russia and now Ukraine. He has a balanced, nuanced approach, always telling when he is stating his own opinions or when an information he presents is not or only to an extent corroborated.)