Reddit reviews Algebra: Volume I

I woke up at 4am, feed the cat, went to sleep.

Now I'm doing formal programming, again. I found an algebra book and now trying to put it into computer such way that it can prove that the statements are correct. It's actually fun.

I'm on 2nd page of chapter 1.1 now, it took me two days to prove that {x}∪{a,b,c....} ⊆ {a,b,c....} (i.e. a set with an added element is a subset of itself).