Gudkov's conjecture
In real algebraic geometry, Gudkov's conjecture, also called Gudkov’s congruence, was a conjecture, and is now a theorem, which states that an M-curve of even degree obeys the congruence
where is the number of positive ovals and the number of negative ovals of the M-curve.
The theorem was proved by the combined works of Vladimir Arnold and Vladimir Rokhlin.
