Ronnie Brown
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 May17 comment How to compute the fundamental group of $S^2 / A$, where $A$ is a finite set of points? You might have a look at arXiv:1404.0556 for a recent use of groupoids. There are not many texts which mention free groupoids on (directed) graphs, an obvious enough idea in this day and age. Good luck! May17 revised Best book for topology? corrected a link and added one May16 revised How to compute the fundamental group of $S^2 / A$, where $A$ is a finite set of points? added a link to mathoverflow May16 revised How to compute the fundamental group of $S^2 / A$, where $A$ is a finite set of points? clarified a reference May16 answered How to compute the fundamental group of $S^2 / A$, where $A$ is a finite set of points? May14 answered Product of CW complexes question May11 answered Homotopy equivalence between $X/A$ and $X$? May11 revised Homotopy equivalence of certain kinds of adjunction spaces added a lnk May11 revised Mayer-Vietoris Type Sequence For Pushouts typo May5 comment Reviewing the basics of algebraic topology for further deeper study Relevant to this discussion is the use of groupoids as more poowerful than groups in algebraic topology. See the discussion at mathoverflow.net/questions/40945/… May4 comment Text similar to chapter 9 of Topology from James Munkres I wonder why so many algebraic topology books ignore the arguments for groupoids and more than one base point as presented for example in mathoverflow.net/questions/40945/…. I also find the arguments for some treatment of knots compelling, since the examples are so clear to students, and also to children and non mathematicians. See the web page www.popmath.org.uk for some knot sculptures and a knot exhibition. May3 comment Reviewing the basics of algebraic topology for further deeper study See also the discussion on math.stackexchange.com/questions/778483/… May2 revised Text similar to chapter 9 of Topology from James Munkres explains paths of various lengthss May2 answered Text similar to chapter 9 of Topology from James Munkres Apr30 comment Does the pullback of a covering space correspond to the pullback of the corresponding representation of $\pi_1$? You can avoid the base points if you use the description of covering maps of spaces in terms of covering morphisms of groupoids, as described in my book "Topology and Groupoids". This applies in particular to pullbacks. Apr28 comment Necessary and sufficient condition for existence of a deck transformation Since algebraic topology is about modelling topology by algebra, it should be pointed out that the theory of covering spaces is well modelled by the theory of covering morphisms of groupoids. See expositions of the latter in Higggins' book "Categories and groupoids" (tac.mta.ca/tac/reprints/articles/7/tr7abs.html) and my book "Topology and groupoids" (amazon). Apr25 comment Suggestion about Algebraic Topology talk Good! What I have found fun is the pentoil trick, which you will find on my talk at Liverpool, What is and what should be `Higher dimensional group theory'? Dec 2009. I have travelled many places carrying a copper tubing pentoil and trefoil, and a nice length of rope, and brought members of the audience out to help with taking the loop off the knot. The knots themselves were made by a University workshop. And of course the relations at a crossing are really an application of SvKT. See also pages.bangor.ac.uk/~mas010/outofline/motion.html#motion . Apr25 revised Suggestion about Algebraic Topology talk added more information Apr24 revised Suggestion about Algebraic Topology talk added the notion of "anomaly" Apr24 answered Suggestion about Algebraic Topology talk