 Abstract Algebra by Dummit & Foote
 The Theory of Algebraic Numbers by Pollard & Diamond
 Introduction to Semigroups by Petrich

What is this?
On these pages you will find a slowly growing (and poorly organized) list of proofs and examples in abstract algebra.
No doubt these pages are riddled with typos and errors in logic, and in many cases alternate strategies abound. When you find an error, or if anything is unclear, let me know and I will fix it.

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Send email to "project (dot) crazy (dot) project (at) gmail (dot) com". 
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It is wonderful that math hobbyists and other persons working alone on Dummit and Foote’s Algebra can now have access to answers to the exercises.
Used properly the answers make working the exercises worthwhile as you can get guidance on teh approach and check your reasoning – something that is impossible for those working alone without a lecturer or tutor to help. Thus the answers are a truly wonderful resource!
peter
Thanks! That’s one of the reasons why I bother to put this online.
I like to work through books by myself, and I strongly recommend that anyone who wants to learn math do the same. If I write down my solutions in notebooks and put them on a shelf next to my desk, they help only me and maybe anyone I can personally help. But if I put them online, maybe other people can get useful ideas from them as well, people I don’t know and will never meet. That’s also partly why I don’t mind that most of the correspondence I get is from people pointing out my errors it lets me know people are reading and understanding.
You make me want to do the same thing. I think it is a good idea to “master” a textbook; perhaps not D&F, but certainly some textbook.
Anyway, probably the most useful site on the web when it comes to studying undergrad abstract algebra. Such sick props for the dedication. Are you a grad student? If not, even bigger props (where do you find time?!).
Best,
Michael
Agreed!
This is indeed a great resource. Thanks for posting everything!
One point I might make regarding the organization of the site:
It would be extremely handy to have the chapter, section, and number of the exercise in the title of the solution post, since many of your solutions refer to previous exercises that readers may want to look up in the book.
It’s probably too much of a pain to add this to old posts, but perhaps it could be included in future posts?
Thanks for this site! I been thinking about a problem all day long I’m supposed to give a proof or counterexample. With deadline looming I searched online and found this site. Would be nice if we could all figure out everything we’re supposed to know but we’re not all Gauss or Euler reincarnated.
HI
For another person slogging thru D and F, the worked examples are much appreciated. I cannot over emphasise the importance of going thru the whole book. If you are just doing exams, then the motivation is primarily strategic: ie get thru the exam. If you are working on a larger project, then doing the whole book and all the examples is the only way to cover what you don’t know (or uncover, more correctly). And looking at another persons working is humbling, exhilarating and at times a relief.