Heawood conjecture

== English == === Etymology === Formulated in 1890 by Percy John Heawood. === Proper noun === the Heawood conjecture (graph theory) A conjecture (proven in 1968) that gives a lower bound for the number of colors that are necessary for graph coloring on a surface of a given genus. ==== Related terms ==== Heawood number ==== See also ==== Ringel-Youngs theorem