Topological properties of differentiable manifolds
Hassler Whitney · Bulletin of the American Mathematical Society · 1937
An address delivered before the Society on September 9, 1937, in State College, by invitation of the Program Committee.f The first space forms the group G z of rotations in 3-space; it is homeomorphic with projective 3-space P 3 .The second space is homeomorphic with the total space (see §2) of the tangent vector space of the projective plane P 2 , or of the 2-sphere S 2 if we use oriented lines.This is easily seen by considering together all parallel lines.Î Differentiable will always mean continuously differentiable.