1. Formal statement

2. References

The Hopf theorem is a statement in differential topology, saying that the topological degree is the only homotopy invariant of continuous maps to spheres.

Formal statement

Let M be an n-dimensional compact oriented manifold and Sⁿ the n-sphere and be continuous. Then if and only if f and g are homotopic.

References

• {{cite book|author=Milnor, J. W.|authorlink=John Milnor|title=Topology from the Differentiable Viewpoint|publisher=Princeton University Press|year=1997|isbn=978-0-691-04833-8}}

• Len Slye
• Lensman: Secret of The Lens
• Len Smith
• Len Smith (footballer)
• Len Smith (footballer, born 1882)
• Len Smith (footballer, born 1913)
• Len Smith (marbles player)
• Len Smith (swimmer)
• Len Smith (trade unionist)
• Lens (movie)
• Lens, Nicholas
• Lenson
• Lenson, Michael
• Len Southward
• Lens regeneration
• Lens replacement surgery
• Lenssen
• Lenssen Nagar
• Lenssen Nagar Areal
• Lens shift
• Lens Technology
• Lens (The Leftovers)
• Lenstore
• Lenstra elliptic curve factorization
• Len Strickland