2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/73483The construction of the COMBINATORIAL data for a surface with n vertices of maximal genus is a classical problem: The maximal genus g=[(n-3)(n-4)/12] was achieved in the famous ``Map Color Theorem'' by Ringel et al. (1968). We present the nicest one of Ringel's constructions, for the case when n is congruent to 7 mod 12, but also an alternative construction, essentially due to Heffter (1898), which easily and explicitly yields surfaces of genus g ~ 1/16 n^2. For GEOMETRIC (polyhedral) surfaces with n vertices the maximal genus is not known. The current record is g ~ n log n, due to McMullen, Schulz & Wills (1983). We present these surfaces with a new construction: We find them in Schlegel diagrams of ``neighborly cubical 4-polytopes,'' as constructed by Joswig & Ziegler (2000).21 pages; Lecture Notes for Oberwolfach Seminar "Discrete Differential Geometry", June 2004Metric GeometryCombinatorics52B70text