Space · region

Combinatorics

Counting, coloring and arrangement. The Erdős problems live mostly here, and so do the results most often settled by computer search and SAT solvers.

Mathematics Subject Classification: 05, 06.

Problems

Four color theorem (solved)
Ramsey number R(5,5) (open)
Hadwiger–Nelson problem (partial)
Union-closed sets conjecture (partial)
Boolean Pythagorean triples problem (solved)
Kahn–Kalai conjecture (solved)

Part of Mathematics.

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