Daniel R. Grayson

```tex \newcommand*{\US}[1]{\USym #1}%changes e.g f^\abstr changed to to Uf ``` Only one is needed.

tiny subscript nearly illegible

1

My eyes can't really make out the tiny subscript on the BF here:

Bjorn would like an image that illustrates what the map on tori RR^2/ZZ^2 given by the map {{1,1},{0,2}} does. I propose representing the map by starting with an image in...

symmetry of \Set

8

We have this: I was going to change the second phrase to "any symmetry is a symmetry of a set", since a symmetry of \Set would be a path from...

Galois groupoid

2

What about skipping the Galois group and introducing the Galois groupoid, instead? Is there any reason to artificially single out a particular splitting field?

definition of subgroup

4

Consider this: I propose to start more gently, with words, and to say that a subgroup of G is a monomorphism from a group to G. After that, to introduce...

quotient groups

2

Wouldn't it make sense for quotient groups to be defined in the way strictly dual to the way subgroups are defined? Here are the two definitions: Then the connection with...

Look at this: I think we need more coercions if we want the type `\bn n` to be regarded as an element of all three of those types.

Is there a definition of "Cayley diagram" in the literature that makes the last sentence of this paragraph true? (This is about ZTors.tex.)

crystallographic groups

1

I wonder whether to write a chapter on crystallographic groups. Here are some references: https://www.jstor.org/stable/2974820 https://www.amazon.com/X-ray-Crystallography-Gregory-S-Girolami/dp/1891389777 https://en.wikipedia.org/wiki/Space_group