1806-1895

English mathematician whose most important work involved various aspects of polyhedra (shapes with multiple sides). His other work involved group theory and, in his late 70s, the theory of knots. However, despite his many serious contributions to mathematics, Kirkman is perhaps best known for the "Fifteen Schoolgirls Problem," in which he states, "If fifteen young ladies of a school walk out three abreast for seven days in succession: it is required to arrange them so that no two shall walk abreast more than once."