At this point Lissitzky subscribed fully to suprematism and, under the guidance of Malevich, helped further develop the movement. In 1919–1920 Lissitzky was a head of Architectural department at the People's Art School where with his students, primarily Lazar Khidekel, he was working on transition from plane to volumetric suprematism. Lissitzky designed On the New System of Art by Malevich, who responded in December 1919: "Lazar Markovich, I salute you on the publication of this little book". Perhaps the most famous work by Lissitzky from the same period was the 1919 propaganda poster "Beat the Whites with the Red Wedge". Russia was going through a civil war at the time, which was mainly fought between the "Reds" (communists, socialists and revolutionaries) and the "Whites" (monarchists, conservatives, liberals and other socialists who opposed the Bolshevik Revolution). The image of the red wedge shattering the white form, simple as it was, communicated a powerful message that left no doubt in the viewer's mind of its intention. The piece is often seen as alluding to the similar shapes used on military maps and, along with its political symbolism, was one of Lissitzky's first major steps away from Malevich's non-objective suprematism into a style his own. He stated: "The artist constructs a new symbol with his brush. This symbol is not a recognizable form of anything that is already finished, already made, or already existent in the world – it is a symbol of a new world, which is being built upon and which exists by the way of the people."In January 17, 1920, Malevich and Lissitzky co-founded the short-lived Molposnovis (Young followers of a new art), a proto-suprematist association of students, professors, and other artists. After a brief and stormy dispute between "old" and "young" generations, and two rounds of renaming, the group reemerged as UNOVIS (Exponents of the new art) in February. Under the leadership of Malevich the group worked on a "suprematist ballet", choreographed by Nina Kogan and on the remake of a 1913 futurist opera Victory Over the Sun by Mikhail Matyushin and Aleksei Kruchenykh. Lissitzky and the entire group chose to share credit and responsibility for the works produced within the group, signing most pieces with a black square. This was partly a homage to a similar piece by their leader, Malevich, and a symbolic embrace of the Communist ideal. This would become the de facto seal of UNOVIS that took the place of individual names or initials. Black squares worn by members as chest badges and cufflinks also resembled the ritual tefillin and thus were no strange symbol in Vitebsk shtetl.The group, which disbanded in 1922, would be pivotal in the dissemination of suprematist ideology in Russia and abroad and launch Lissitzky's status as one of the leading figures in the avant garde. Incidentally, the earliest appearance of the signature Lissitzky (Russian: Эль Лисицкий) emerged in the handmade UNOVIS Miscellany, issued in two copies in March–April 1920, and containing his manifesto on book art: "the book enters the skull through the eye not the ear therefore the pathways the waves move at much greater speed and with more intensity. if i (sic) can only sing through my mouth with a book i (sic) can show myself in various guises."

Question: Who worked on transition from plane to volumetric suprematism?
Answer: Lissitzky