rotation systems and 2-cell-embeddings was first settled in a dual form by Lothar Heffter in the 1890s and extensively used by Ringel during the 1950s. Independently...
9 KB (1,102 words) - 21:51, 23 September 2024
and Judith (born 1943). Peltesohn solved the Difference Problems of Lothar Heffter [de] (1896) in combinatorics in 1939. A Difference Triple (a, b, c)...
5 KB (499 words) - 10:36, 10 November 2023
Alfred Kempe in 1879, and extended to maps on non-planar surfaces by Lothar Heffter [de] in 1891. Duality as an operation on abstract planar graphs was...
51 KB (6,607 words) - 17:51, 27 September 2024
field as a module over its abelian Galois group (cf Iwasawa theory). Lothar Heffter, Ludwig Stickelberger, Jahresbericht der Deutschen Matematische Vereinigung...
7 KB (468 words) - 19:28, 23 September 2024
1090/s0002-9904-1944-08150-0, MR 1564626, available from Project Euclid. Heffter, Lothar (1943), "Oskar Bolza", Jahresbericht der Deutschen Mathematiker-Vereinigung...
13 KB (1,360 words) - 19:40, 26 October 2024