| In particular he made contributions of major importance in the theory of polytopes, non-euclidean geometry, group theory and combinatorics. |
| His early works range over number theory, statistics, combinatorics, game theory, as well as his principal interest of commutative algebra. |
| The problems which attracted him most were problems in combinatorics, graph theory, and number theory. |
| His basic research contributions span complex analysis, mathematical physics, probability theory, geometry, and combinatorics. |
| His work led to considerable activity in the new area of algebraic combinatorics. |
| His interests were mainly in number theory and combinatorics, though they ranged into topology and other areas of mathematics. |
