[2-factor theorem](https://en.wikipedia.org/wiki/2-factor_theorem) [Tutte-Berge formula](https://en.wikipedia.org/wiki/Tutte%E2%80%93Berge_formula) https://math.stackexchange.com/questions/4042360/tutte-berge-formula-simple-proof-clarification Note that we do have [Tutte's theorem](https://leanprover-community.github.io/1000.html#Q510197).
2-factor theorem
Tutte-Berge formula
https://math.stackexchange.com/questions/4042360/tutte-berge-formula-simple-proof-clarification
Note that we do have Tutte's theorem.