Eric Shapiro

38 posts
Apr 20, 2017

Sequences, Hausdorff Spaces and Nets

Sequences, Hausdorff Spaces and Nets

I'm now going to talk about sequences and nets, which often provide an alternative way of describing topological phenomena. I'll also talk about Hausdorff spaces, which have all sorts of nice properties.

Apr 9, 2017

Quotient Spaces

Quotient Spaces

The notion of a quotient space will effectively allow us to glue pieces of topological spaces together. This corresponds to the collapsing of equivalent subsets to points which occurs in quotient sets, as I mentioned in my last post.

Apr 8, 2017

Equivalence Relations and Quotient Sets

Equivalence Relations and Quotient Sets

Quotient sets of $A$ are comprised not of elements of $A$, but of the equivalence classes they fall into. This gives us a powerful method to collapse a set into a smaller set that is in some way still representative of the original set.

Apr 8, 2017

Product Spaces

Product Spaces

Next let's talk about an intuitive way to combine topological spaces to create new spaces which inherit certain characteristics from their parents. We've talked about Cartesian products before in the context of set theory, but what happens if we take the Cartesian product of topological spaces?

Apr 8, 2017

Subspaces

Subspaces

A topological space is, at its core, just a set with some additional structure. So what if we want to keep the structure, but change the underlying set? There's an easy and somewhat obvious way to do this.

Apr 7, 2017

Continuity and Homeomorphisms

Continuity and Homeomorphisms

The concept of continuity is central to the study of topology. So much so, in fact, that whenever anyone talks about a map between topological spaces, they generally expect you to know that they're talking about a continuous map.

Apr 7, 2017

Groups and their Basic Properties

Groups and their Basic Properties

Essentially, a group is a set endowed with a very basic structure. This structure is enforced by an operation which governs how the elements in the group interact with each other.

Apr 2, 2017

Bases for Topologies

Bases for Topologies

Essentially, a basis is a 'small' collection of open sets from which every open set can be easily generated. It is often useful to talk about the topology generated by a specific basis, since many facts about a topology can be gleaned by studying one of its bases.

Mar 31, 2017

A First Look at Topological Spaces

A First Look at Topological Spaces

There are also many circumstances in which we care about the shape of a space but couldn't care less about distances. For instance, a famous puzzle that influenced the development of the entire field of topology is the problem of the **Seven Bridges of Königsberg**.

Mar 31, 2017

Metric Spaces (2)

Metric Spaces (2)

Looking back through my first post about metric spaces, it occurred to me that I should probably have emphasized a few things that could be a bit confusing, so let me address those first before pressing forward.