Categories

Category Theory (Oxford Logic Guides)
$155.00
This book is nice in that, once understood, it provides a quick introduction to category theory that gets to the pith of the matter right away. The author chooses illuminating examples and provides (what seems to me to be) the right amount of discussion for each topic (not too rambling, leaving the reader bored, and not to terse, leaving him confused).

However, the author was quite careless in keeping his notation and terminology comprehensible. A common problem is the reference to two different entities by the same name in situations in which it's important to distinguish between the two. For example, the author sometimes uses 'product' to mean the object that has the mapping property of the product of objects A and B and sometimes he uses it to refer to A, B, their product object, and the relevant arrows. Similarly for equalizers. Also annoying is the author's tendency to switch notation mid-proof without any notice. The author also has several unexplained uses for 'Hom(x,y)' that differ greatly.

These problems can be overcome. Once one finds out what's really meant, the text is actually quite helpful. However, I read this book on my own without access to anyone who knew anything about the theory, making it rather difficult to clarify the author's terminology.

In short, it's a book that is good on content but bad on form. I'd recommend starting with the (free) resources listed on the Wikipedia page for category theory, which, as of this writing, have less material but better presentation.

Wipe Off Sentence Strips (TEPT4001) Category: Classroom Supplies
$5.49
I ordered this item because I was no longer able to find it at my local stores. I received the item quickly and at a great price.

Categories On the Beauty of Physics : Essential Physics Concepts and Their Companions in Art and Literature
$24.95
This is a great concept: illustrate principles of physics using art and nature. Unfortunately, the execution is poor. The book's layout is dull, and the whole thing comes across as boring rather than fascinating. I had hoped to share it with someone who doesn't like science, but couldn't, because it would have turned him off even more. A great disappointment.

Clear Polyethylene Food Handling Gloves Large (GLX370L) Category: Disposable Miscellaneous Gloves
$8.54
These gloves were perpect for a Halloween craft at school where we filled them with popcorn after putting a candy corn in each finger for nails. Kids loved it and fun was had by all.....