*In which we prove Lagrange’s theorem, and deduce many interesting results as a consequence.*

## Groups and Group Actions: Lecture 8

March 9, 2017## Groups and Group Actions: Lecture 7

March 8, 2017*In which we think about the link between equivalence relations and partitions, and meet cosets.*

## Groups and Group Actions: Lecture 6

March 2, 2017*In which we think about cyclic groups, and renew an old friendship with equivalence relations.*

## Groups and Group Actions: Lecture 5

March 1, 2017*In which we find that the alternating group is a group, and study subgroups in more detail.*

## Groups and Group Actions: Lecture 4

February 23, 2017*In which we explore permutations in more detail.*

## Groups and Group Actions: Lecture 3

February 22, 2017*In which we start to explore permutations.*

## Groups and Group Actions: Lecture 2

February 16, 2017*In which we meet the dihedral groups, build new groups from old, and explore Cayley tables.*

## Groups and Group Actions: Lecture 1

February 15, 2017*In which we learn what a group is, and meet many examples.*

## Groups and Group Actions: Lecture 0

February 14, 2017Welcome to the course blog for the Oxford first year Groups and Group Actions course (Hilary and Trinity Terms 2017). I hope that this will be a useful resource to accompany the lectures, problems sheets and tutorials. Please check back after each lecture for a new post. In addition, I have a course page with some useful information, and you will also want to visit the official department course page (with problems sheets, for example). My YouTube channel hedgehogmaths has some videos that you might find helpful when revising the course.

The plan is that I’ll put up a new post just after each lecture. Each post will have a quick summary of the topics covered in that lecture, with suggestions for further reading, plus one or more problems to get you thinking about the topics that will be covered in the next lecture. Please do try these problems, as they will help you to get the most from the lectures (even if you don’t solve a problem, thinking about it will still be useful). Doing a bit of thinking in advance can save you time in the long run, because you’ll understand more of the lecture at the time. There will also be exercises that you can try to check your understanding of that day’s lecture. Again, please do try these, as they will help you to work actively on your lecture notes and will get you thinking in the right way to tackle the problems sheets.

You are very welcome to leave comments (for me and for your fellow students) on each post. For example, you might have your own suggestions for good places to read about the topics, or you might have another way to look at one of the ideas, or you might have a really good example that illustrates some interesting aspect of the material, or you might have a question that you’d like to raise.

Of course, now I have to suggest something to think about before Lecture 1! So here it is. If you haven’t come across a definition of a group before, then you could do some quick reading, for example this very accessible NRICH article. How many examples of groups have you come across in the Oxford course so far? (Hint: you’ve met lots!) Think of as many as you can, it’s really helpful when learning group theory to have many examples of groups in mind.

## Groups and Group Actions: Lecture 16

May 18, 2016*In which we meet Cayley’s Theorem and reach the end of this particular adventure, but catch a glimpse of far-off lands still to be explored.*