This video illustrates the proof of the Theorem in the title. The proof goes like this:
Consider a rectangle. Then the path going up the left side of the rectangle and then along the top is homeo...
This video illustrates the proof of the Theorem in the title. The proof goes like this:
Consider a rectangle. Then the path going up the left side of the rectangle and then along the top is homeomorphic to the path going first along the bottom and then up the right side.
Gluing the rectancle to make a torus, this shows that going first around through the hole and then along the outside is homeomorphic to going first along the outside and then through the hole.
Since these two path generate the fundamental group of the torus this proves that this group is abelan. q.e.d.
Remark: This is a very special property. Many topological spaces have nonabelian fundamental groups.
This video was produces for a topology seminar at the Leibniz Universitaet Hannover.
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not exactly related to what the vid. is about, but wouldn't it be something similar to two trapezoids short-side-joined-together are required to make a torus, otherwise when it wraps the inner area is going to have loads of excess overlaps. i don't do higher-dimensional toplogy i just find it fascinating how people can think of processes (formulas) that describe actual-size wrapping of surfaces. but then it's likely textiles and measure knew all that, in the old ways (proportions to each other).
But this transformation isn't contunuous (as homotopy must be), it cut the connetion point and change the connect components (if get of a point) in the start
The video would be more effective if it had audio which: Defines what a group is; Then shows what the group elements are for this topological situation; Then points out that it is an Abelian (commutative) group
You may be thinking of the figure eight space -- two circles joined together at a point. The fundamental group of a figure eight space is the free product of Z with itself. BTW, if you puncture the torus, i.e. delete a point, then the result is homotopy equivalent to a figure eight space, and so has the same fundamental group. You can see how the "missing point" would get in the way of the homotopy in the video.
Much easier to show that the torus is homeomorphic to S^1*S^1 and then remember that the fundamental group is a topological property. I like these videos though, I'm so bad at picturing this stuff.
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