Grinberg's theorem
On Hamiltonian cycles in planar graphs / From Wikipedia, the free encyclopedia
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In graph theory, Grinberg's theorem is a necessary condition for a planar graph to contain a Hamiltonian cycle, based on the lengths of its face cycles. If a graph does not meet this condition, it is not Hamiltonian. The result has been widely used to prove that certain planar graphs constructed to have additional properties are not Hamiltonian; for instance it can prove non-Hamiltonicity of some counterexamples to Tait's conjecture that cubic polyhedral graphs are Hamiltonian.
Grinberg's theorem is named after Latvian mathematician Emanuel Grinberg, who proved it in 1968.