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An attempt to motivate the definition of a topology.

Many people first learn about topology as a generalization of a metric space. We can observe that the open sets of a metric space obey three rules: The entire space is open, as well as the empty set The intersection of finitely many open sets is open The arbitrary union of open sets is openContinue reading “An attempt to motivate the definition of a topology.”

A proof that there exists an infinite collection of sets whose cartesian product is nonempty.

I stumbled upon this succinct proof while discussing topology with some friends. Suppose that, for any infinite collection of sets , the cartesian product, i.e. the collection of all choice functions on , is empty. I claim this implies Tychonoff’s theorem, which states that the product of any collection of compact topological spaces is aContinue reading “A proof that there exists an infinite collection of sets whose cartesian product is nonempty.”

Using the Seifert-van Kampen theorem to calculate the fundamental group of the torus, aided by illustrations from mspaint

One of my favorite theorems is the Seifert-van Kampen theorem. It’s a very handy result in algebraic topology which allows us to calculate the fundamental group of complicated spaces by breaking them down into simpler spaces. The version of the theorem I’ll be using here can be stated as follows: Let be a path connectedContinue reading “Using the Seifert-van Kampen theorem to calculate the fundamental group of the torus, aided by illustrations from mspaint”

A Classic Joke Proof

While this may stretch the stated point of this blog, I’m ultimately the one in control, and I’ll decide what gets posted here. And I think it’s really funny and would be fun to write up. I am nowhere near the first person who has ever told this joke. For all , . For realContinue reading “A Classic Joke Proof”

Every set has a minimal superset

I credit Mikey and Atal with this proof. For any set which is a subset of a (lets say much larger) set , a minimal superset of is a set such that , and if , then for any superset of . I claim that any set has a minimal superset. We see this byContinue reading “Every set has a minimal superset”

Showing two easy spaces are not homeomorphic.

This one is my own doing. I will be showing the following: is not homeomorphic to First, we begin with a definition and a lemma. If is any topological space, we define the of as the topological space We have the following lemma: if are two homeomorphic topological spaces, then their one point compactifications areContinue reading “Showing two easy spaces are not homeomorphic.”