Complements of Curves in Closed Surfaces: Homeomorphic?

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Discussion Overview

The discussion revolves around the homeomorphism of surfaces obtained by removing non-isotopic curves from a compact, oriented surface. Participants explore the conditions under which the resulting surfaces remain homeomorphic, particularly focusing on the implications of isotopy and homology.

Discussion Character

  • Technical explanation, Debate/contested

Main Points Raised

  • One participant asserts that the statement regarding homeomorphism of surfaces after removing non-isotopic curves is incorrect, providing examples to illustrate this point.
  • Another participant suggests that the correct result may be found in a specific mathematical text, indicating a potential source for clarification.
  • A link to a document is shared, which purportedly contains relevant information about the conditions for homeomorphism related to simple-closed curves.
  • It is noted that the homeomorphism may hold if the curves are isotopic or homologous, but this remains uncertain.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correctness of the original statement regarding homeomorphism after removing curves, and multiple competing views remain regarding the conditions under which the result holds.

Contextual Notes

The discussion highlights potential limitations in understanding the relationships between isotopy, homology, and homeomorphism, as well as the need for precise definitions in the context of the problem.

WWGD
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Hi, let ## \alpha, \gamma ## be non-isotopic curves in a compact, oriented surface S. There is a result to the effect that ## S-\alpha## is homeo. to ## S- \gamma ## . This is not true as stated; we can , e.g., remove a disk (trivial class) in a copy of S and then remove a meridian ( a generator of ## H^1 (T^2) ##). Does anyone know the corrected result? This is not true either if we only remove essential curves. It seems like if ##\alpha, \gamma## actually _were_ isotopic , then this would be true. Or maybe if they were homologous?
Thanks.
 
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I seem to remember coming across the result you are looking for in Farb and Margalit's Primer on Mapping Class Groups, in chapter 1, if I am not mistaken. I think maybe they call it the change of coordinates principle.
 
http://www.math.ethz.ch/~bgabi/Farb%20Magalit%20January%202011%20version.pdf
 
Last edited by a moderator:
Thanks; in case anyone else is interested, here it is, towards the bottom of p.39:

There is an orientation-preserving homeo. of a surface S taking one s.c.c * ## \gamma## to ## \beta## iff the
corresponding cut surfaces ##S -\gamma ## , ##S- \beta ## are homeomorphic.

*s.c.c: Simple-Closed Curve.
 

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