## Undergraduate Topology

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I am developing an introductory topology course for undergraduates, and I am wondering what topics to cover. At my institution, real analysis is not a prerequisite for the course, so it is more than likely that the intended audience has not been exposed to this material. Does anyone have any suggestions?

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## 7 Answers

I've found that doing low-dimensional manifold topology is very appealing to undergraduates. I used the "Topology Now!" text by Messer and Straffin and, while the text isn't perfect, the approach was wonderfully successful.

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I second the suggestion to focus on low-dimensional topology. Some particularly fun parts of low-dimensional topology for a first course are: classification of surfaces (including Part 1 of Conway et al "Symmetry of Things"); some baby knot theory (Reidemeister moves, quandle invariants like the number of three-colorings of the knot diagram, and also some invariants that are not diagram-based). It is also worth telling the students without proof that intuition from low dimensions often fails as you move higher up. Exotic smooth structures and non-smoothable manifolds come to mind. – Theo Johnson-Freyd Aug 22 at 17:57

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I second Aeryk's suggestion to focus on low-dimensional topology. More generally, I think that algebraic topology can be more exciting than point-set topology.

That said, when I was an undergraduate, I do remember being quite excited about the Bourbaki program and point-set definitions and so on. I remember one "first course in topology" that alternated days: low-dimensional topology on even days and point-set on odd. Except the point-set portion began with set theory, cardinal and ordinal numbers, and the axiom of choice; then moved on to metric spaces; and only then introduced point-set topology. I basically think that to motivate the point-set definitions, you had better start with metric spaces.

If on the other hand you focus more on broadly-defined algebraic topology, then in addition to the low-dimensional topology of manifolds (surfaces, knots, etc.), another good topic is Brower fixed-point theorem as an application of fundamental group functor on pointed spaces. Perhaps, if you are very ambitious, you can prove that 2dTQFT = commmutative Frobenius algebra, and talk more generally about cobordism equivalence. Oh, and especially given the recent sad news, be sure to include a little Morse theory and Outside In.

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+1 for "to motivate the point-set definitions, you had better start with metric spaces. (I'm not saying you should do point-set topology, but that if you do it, metric spaces should come first.) – Andreas Blass Aug 22 at 22:57

In the 1970s I developed an undergraduate course on knots, (source book was by Crowell and Fox) to replace general topology and homology, as it was very easy for students to understand the point of the course, there were interesting relations with group theory, and lots of specific calculations and other things to do. The course was eventually taken over by others, and resulted in a book,

Knots and Surfaces, by N.D. Gilbert and T. Porter

which had good reviews.

For me, it led to giving popular talks on "How mathematics gets into Knots", and eventually to the exhibition you can see on the web site for the Centre for the Popularisation of Mathematics. In these talks I could also talk about mathematics, including, for example, the importance of analogy in mathematics. This led to one boy at a talk for children, some aged 12, asking: "Are there infinitely many prime knots? " Wow! So giving this undergraduate course has led to all sorts of fun and rewarding things! My copper pentoil knot used with string to demonstrate the ideas of the fundamental group has also travelled to many countries, see for example the pdf of a William J. Spencer Lecture in Kansas, April, 2012.

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Ronald,you don't get enough credit for your very inventive and original attempts to reform a basic course in topology. You should get more.  – Andrew L Nov 18 at 5:07

I think you could do a lot worse than to focus on modern applications by using the texts of Edelsbrunner and Harer and/or Zomorodian as touchstones and an avenue towards current work in topological data analysis. These books are self-contained treatments that focus on Morse theory and homology over $\mathbb{Z}/2\mathbb{Z}$, and there are a lot of materials and software available for a course to be built from.

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As a resource for low-dimensional topology, I would suggest The shape of space by Jeffrey Weeks. It covers how to build compact two-manifolds and some three manifolds. Exercises include playing tic-tac-toe on surfaces and forming sums of surfaces. It then moves on to some three dimensional topology with a heavy focus on attempting to visualize the spaces.

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We give a Geometry and Topology course at Macquarie for students with no real analysis, using notes written by a colleague. Here is the homepage for the course, so you can get an idea of what we do.

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If the intent is to provide breadth, then many of the suggestions others have made are quite appealing, especially if it is made clear what branches of topology are being introduced and what a student should do outside of class to develop depth in any or all of the branches.

If the intent is to provide depth, there are likely several texts out there, one for each branch, with suggestions. I remember covering Munkres first course in Topology starting with chapter 2; even though we skipped over the set theory and foundations, I was intrigued enough by them to study set theory and foundations while in graduate school. Although the class did not go all the way through the book that first semester, we got exposed to quite a bit, and I developed more ofa taste for formalism from that class more than from any other that I took as an undergraduate.

If the intent is to provide both depth and breadth, I suggest part of it be run as a student seminar. A later toplogy course I took had me present Sard's theorem; if nothing else came from that course I at least know how to prepare to explain Sard'd theorem for my next opportunity.

Gerhard "And This Was Decades Ago" Paseman, 2012.08.22

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