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Regular values of immersion.

  1. Mar 13, 2009 #1

    WWGD

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    Hi:
    This problem should be relatively simple, but I have been going in circles, without
    figuring out a solution:

    If f:X->R^2k is an immersion

    and a is a regular value for the differential map F_*: T(X) -> R^2k, where

    F(x,v) = df_x(v). Then show F^-1 (a) is a finite set.

    I have tried using the differential topology def. of degree of a map , where we calculate

    the degree by substracting the number of points where the Jacobian has negative

    determinant (orientation-reversing) minus the values where JF has positive determinant.

    I think I am close, but not there.

    Any Ideas?

    Thanks.
     
  2. jcsd
  3. Mar 13, 2009 #2

    WWGD

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    Is it enough to say that for regular values, since f is a local diffeomorphism, it is

    a covering map?. ( but we could always have infinitely many sheets in the cover...)
     
  4. Mar 20, 2009 #3
    Your question confuses me. An immersion I think by definition has all regular values. It Jacobian is a maximal rank everywhere. Maybe you are using a different definition of regular value.

    You are right that since your map is a local diffeomorphism the inverse image of any point must be discrete. If X is compact then any discrete subset must be finite. If X is not compact this is not true. For instance the covering of the circle by the real line x -> exp(ix) is an immersion but the inverse image of each point is infinite.
     
    Last edited: Mar 20, 2009
  5. Mar 20, 2009 #4

    WWGD

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    "Your question confuses me. An immersion I think by definition has all regular values. It Jacobian is a maximal rank everywhere. Maybe you are using a different definition of regular value."

    I was just considering the immersion to be in "standard position" for the inverse image
    of a regular value to be a manifold, but I admit I did not explain that clearly.

    Still, please put up with some innacuracies for a while, since I am still an analyst in Algebraic topology exile. Hope not for too long
     
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