Heinrich Tietze

Heinrich Franz Friedrich Tietze was an Austrian mathematician, born on 31 August 1880 and died on 17 February 1964, famous for the Tietze extension theorem on functions from topological spaces to the real numbers. He also developed the Tietze transformations for group presentations and was the first to pose the group isomorphism problem. Tietze's graph is also named after him. It describes the boundaries of a subdivision of the Mobius strip into six mutually adjacent regions, and Tietze found it as part of an extension of the four color theorem to non-orientable surfaces.