I'm reading a book on abstract algebra and although it's good to read the proofs, I keep wishing there was a summary of the book without the proofs, so that I can consult it when needed. I think that if it is a good idea for this book, then it may be a good idea for all the mathematical subjects and if it is such a good idea, then it probably already exists.
Ideally, each definition would have links to the definitions on which it depends.