A difficulty in understanding a part of a paragraph in Guillemin & Pollack p.60












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I do not understand the highlighted part of the paragraph given below:



enter image description here



Could anyone explain it for me please?










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    There must be a better way to highlight.
    – Randall
    Nov 28 '18 at 2:54










  • I am sorry @Randall for being unskillful in highligting
    – hopefully
    Nov 28 '18 at 3:41
















0














I do not understand the highlighted part of the paragraph given below:



enter image description here



Could anyone explain it for me please?










share|cite|improve this question


















  • 1




    There must be a better way to highlight.
    – Randall
    Nov 28 '18 at 2:54










  • I am sorry @Randall for being unskillful in highligting
    – hopefully
    Nov 28 '18 at 3:41














0












0








0







I do not understand the highlighted part of the paragraph given below:



enter image description here



Could anyone explain it for me please?










share|cite|improve this question













I do not understand the highlighted part of the paragraph given below:



enter image description here



Could anyone explain it for me please?







general-topology differential-topology manifolds-with-boundary transversality






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asked Nov 28 '18 at 2:43









hopefully

129112




129112








  • 1




    There must be a better way to highlight.
    – Randall
    Nov 28 '18 at 2:54










  • I am sorry @Randall for being unskillful in highligting
    – hopefully
    Nov 28 '18 at 3:41














  • 1




    There must be a better way to highlight.
    – Randall
    Nov 28 '18 at 2:54










  • I am sorry @Randall for being unskillful in highligting
    – hopefully
    Nov 28 '18 at 3:41








1




1




There must be a better way to highlight.
– Randall
Nov 28 '18 at 2:54




There must be a better way to highlight.
– Randall
Nov 28 '18 at 2:54












I am sorry @Randall for being unskillful in highligting
– hopefully
Nov 28 '18 at 3:41




I am sorry @Randall for being unskillful in highligting
– hopefully
Nov 28 '18 at 3:41










1 Answer
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For their example map $f$, we have $f^{-1}(Z) = partial H^2$, which is the $x$-axis in the plane. This is boundaryless, so $partial f^{-1}(Z)$ is empty. On the other hand, $f^{-1}(Z) cap partial H^2 = partial H^2$ which is the $x$-axis and not empty. Hence
$partial f^{-1}(Z) = f^{-1}(Z) cap partial H^2$ is false in this example. Since you would rather have the boundary of the preimage be the part of the preimage that lives in the boundary, you will have to make additional assumptions above and beyond transversality.






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    1 Answer
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    For their example map $f$, we have $f^{-1}(Z) = partial H^2$, which is the $x$-axis in the plane. This is boundaryless, so $partial f^{-1}(Z)$ is empty. On the other hand, $f^{-1}(Z) cap partial H^2 = partial H^2$ which is the $x$-axis and not empty. Hence
    $partial f^{-1}(Z) = f^{-1}(Z) cap partial H^2$ is false in this example. Since you would rather have the boundary of the preimage be the part of the preimage that lives in the boundary, you will have to make additional assumptions above and beyond transversality.






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      For their example map $f$, we have $f^{-1}(Z) = partial H^2$, which is the $x$-axis in the plane. This is boundaryless, so $partial f^{-1}(Z)$ is empty. On the other hand, $f^{-1}(Z) cap partial H^2 = partial H^2$ which is the $x$-axis and not empty. Hence
      $partial f^{-1}(Z) = f^{-1}(Z) cap partial H^2$ is false in this example. Since you would rather have the boundary of the preimage be the part of the preimage that lives in the boundary, you will have to make additional assumptions above and beyond transversality.






      share|cite|improve this answer
























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        2






        For their example map $f$, we have $f^{-1}(Z) = partial H^2$, which is the $x$-axis in the plane. This is boundaryless, so $partial f^{-1}(Z)$ is empty. On the other hand, $f^{-1}(Z) cap partial H^2 = partial H^2$ which is the $x$-axis and not empty. Hence
        $partial f^{-1}(Z) = f^{-1}(Z) cap partial H^2$ is false in this example. Since you would rather have the boundary of the preimage be the part of the preimage that lives in the boundary, you will have to make additional assumptions above and beyond transversality.






        share|cite|improve this answer












        For their example map $f$, we have $f^{-1}(Z) = partial H^2$, which is the $x$-axis in the plane. This is boundaryless, so $partial f^{-1}(Z)$ is empty. On the other hand, $f^{-1}(Z) cap partial H^2 = partial H^2$ which is the $x$-axis and not empty. Hence
        $partial f^{-1}(Z) = f^{-1}(Z) cap partial H^2$ is false in this example. Since you would rather have the boundary of the preimage be the part of the preimage that lives in the boundary, you will have to make additional assumptions above and beyond transversality.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Nov 28 '18 at 2:54









        Randall

        9,12611129




        9,12611129






























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