Being too pedantic with writing proofs

I've looked at your three proofs, but I only analyzed the first one very closely (since the answerers of the last two provided detailed comments on your proofs). I've added an answer to the first question.

You'll notice that in my answer I use a very common lemma: $B \subseteq \cap_{i \in I} A_i$ iff $\forall i \in I \ B \subseteq A_i.$

Everyone learns these kinds of lemmas eventually, usually from reading proofs that use them. Sometimes one discovers them on one's own, but this usually ultimately depends on inspiration from encountering broadly similar arguments in other people's proofs first.

I'm not very familiar with Velleman's book, but from looking at some of it casually, it seems that most of the arguments presented go back to the level of elements rather than using any kind of higher-level lemmas on sets. So you can hardly be blamed for reproducing the same style of proof the author uses.

Your proofs will naturally become more sophisticated when you start reading more sophisticated mathematics. In the meantime, you're doing the right thing by breaking things down so that you understand every detail of a proof. That's the main thing.

Another way you can improve your proofs is by selecting textbooks or problem books with full solutions. That way you can compare your solution with the book's. You seem to have the discipline to do things on your own before looking at a solution, so this is likely to be a help to you, not a hindrance.

Here are my two cents. I've only read the second proof you linked to, and only the first direction of it, and I think it is not too pedantic at all.

The thing it, it all depends on how far gone you are in your mathematical studies and how used to you are, and how comfortable you're with, rigorous proofs. Since you are just beginning studying rigorous mathematics - and self-studying at that - I think it is actually crucial you begin by writing such "pedantic" proofs. Then, once you grow familiar with such proofs and become more confident, you can start writing more 'casual' proofs, because you'd develop an instinct that the proof is really correct and that you could make it completely rigorous if you needed to.

This doesn't stop at your level: the more you study, the less rigorous proofs becomes. And in fact, people often make mistakes, thinking something is obvious and that they could prove it completely rigorously if they wanted to, which then later turns out to be false. But that's just the way these things work, and you have to at least become a little more relaxed at proof-writing, or else you'd never have the time to prove anything more "serious", involving more complex mathematics.

One thing which is perhaps confusing about this is the feeling that you can always be more pedantic. And it's more or less true. I suggest reading about formal languages and formal proofs, if you find this point interesting/confusing. But in my opinion (and most people's) the level of rigor in the proofs you linked to (at least what I read) is enough. Why? Because, usually, when you write at such a level of rigor, even in the beginning of your studies, you don't make mistakes, thinking something is clear while it is in fact incorrect. That is, since your proofs are fairly rigorous (even if they could be even more rigorous), there aren't really too many "subtle" points you might be missing.

This is at least how I see it.

Sharing: I've been given math classes for a long time, so what I'll say is only my own experience.

That "redundancy" you speaks of is as relative as it can possibly be. I'm researching for this exact situation because my work now have to do with the elaboration of materials for students to work basically alone, for themselves, at home, with minimal interaction with tutors. And the answer so far is: there's no perfect way to elaborate any materials like that. There's no perfection in writing something that it will, 100% sure, be satisfactory to every reader. It may be never enough. In this case, I'm just like you. I have this need for detail, give the maximum number of information that is possible to make the reader understand every little thing about the demonstration. What isn't written anywhere is that when we "give" someone an answer for a problem, we give "our" experience with that exact problem, the way "we" saw it. And what the reader will do with that answer is HIS problem, isn't part of the solution that we proposed. Many times my friends ask me: there's any way to resume it, to make it simple? My answer is always: if you understand the answer, you can write it with your own words, put anything that you judge necessary and take off everything you judge that is too much.

But keep one thing in mind: you maybe never be able to know exactly what the person - the one that is asking the question - have on their baggage. So, always put the maximum information that you can, for the good sake of the answer. And when and if someone says it's pedantic, just ignore that, because he probably understood your answer and, in this situation, he fells able to rewrite more efficiently. It means that you have succeeded in this answer, it means a full victory.

That's my point of view, obviously... I remember using a textbook where the autor used to say "the proof is obvious" and skip to the next part, and it always made me feel so stupid for not seeing the "obvious" part. Today I make my own way through the "obvious" and rewrite anything that I judge that need more explanation, and my friends always want my notebooks for further instruction. I'm at some point that I can never throw away an old notebook because there's always someone that needs my notes. And they are always welcome, because math isn't easy anyway, and if I can help, I fell completely honored.

As for my students, I always ask for them to put the maximum information possible, and if they don't know exactly how to say something, that they should describe it with his own words, the best way they can, because with this material and if the answer went through a good place, we can use it and discuss in the class. I've been paying my price. My students sometimes put some long answers, some big text trying to proof their points. So the work reviewing my students classwork is huge... But I like it, and most of the time they understood the basics of it, so I have work to do at the class with them, time to polish the knowledge they have and make them feel comfortable with themselves when writing in math.

That's it. Sorry for the long outburst.