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A differentiable manifold (of class C k) consists of a pair (M, O M) where M is a second countable Hausdorff space, and O M is a sheaf of local R-algebras defined on M, such that the locally ringed space (M, O M) is locally isomorphic to (R n, O). In this way, differentiable manifolds can be thought of as schemes modeled on R n.
The key part of the theorem is a construction of the de Rham homomorphism. [1] Let M be a manifold. Then there is a map : () from the space of differential p-forms to the space of smooth singular p-cochains given by
The Poincaré lemma thus says the rest of the sequence is exact too (since a manifold is locally diffeomorphic to an open subset of and then each point has an open ball as a neighborhood). In the language of homological algebra , it means that the de Rham complex determines a resolution of the constant sheaf R M {\displaystyle \mathbb {R} _{M}} .
A map is a local diffeomorphism if and only if it is a smooth immersion (smooth local embedding) and an open map.. The inverse function theorem implies that a smooth map : is a local diffeomorphism if and only if the derivative: is a linear isomorphism for all points .
Other types of manifolds are formed by adding structure to a topological manifold (e.g. differentiable manifolds are topological manifolds equipped with a differential structure). Every manifold has an "underlying" topological manifold, obtained by simply "forgetting" the added structure. [1] However, not every topological manifold can be ...
A regular homotopy between two immersions f and g from a manifold M to a manifold N is defined to be a differentiable function H : M × [0,1] → N such that for all t in [0, 1] the function H t : M → N defined by H t (x) = H(x, t) for all x ∈ M is an immersion, with H 0 = f, H 1 = g. A regular homotopy is thus a homotopy through immersions.
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Let M and N be differentiable manifolds and : be a differentiable map between them. The map f is a submersion at a point if its differential: is a surjective linear map. [1] In this case p is called a regular point of the map f, otherwise, p is a critical point.