 Rokhlin's theorem

In 4-dimensional topology, a branch of mathematics, Rokhlin's theorem states that if a smooth, closed 4-manifold "M" has a spin structure (or, equivalently, the second Stiefel–Whitney class formula_1 vanishes), then the signature of its intersection form, a quadratic form on the second cohomology group formula_2, is divisible by 16.The theorem is named for Vladimir Rokhlin, who proved it in 1952.