Erdős Problem #715

Does every regular graph of degree $4$ contain a regular subgraph of degree $3$? Is there any $r$ such that every regular graph of degree $r$ must contain a regular subgraph of degree $3$?

#715: [Er75][Er81]

graph theory

A problem of Berge (or Berge and Sauer). Alon, Friedland, and Kalai [AFK84] proved that every $4$-regular graph plus an edge contains a $3$-regular subgraph, and hence in particular every $r$-regular graph with $r\geq 5$ contains a $3$-regular subgraph.

The answer is yes, proved by Tashkinov [Ta82].

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This page was last edited 06 October 2025.

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