Is the second example not a set because it's not denoted by a capital letter? This seems silly; it would've been a set in complex analysis or linear algebra; why not in topology?
>>8109559
time to find a new textbook
>>8109565
pls anon; I already got attached. ;; I read the prefaces and I feel like I got a personal student-teacher connection with the author and when I read the text, I narrate his voice as though he were an actual lecturer so that I don't get lonely.
>>8109559
Oh god what book is this. {1,2,3} is totally a set.
OP, something else to keep in mind. In ZFC (which is probably secretly the axiom system your book is using), everything is a set. The lowercase/uppercase distinction is used as a convention to help one keep track of what objects are being manipulated, and what is containing those objects. This does not change the fact that everything is a set.
>>8109571
This isn't a YLYL thread.
>>8109565
This.
What the fuck are you even trying to learn OP?
Pedantic set theory? Find a book that explains it better. Logic? Find a logic book.
Mathematics with set theory? Get a better book and maybe Rudin.
>>8109577
However, the difference between a "set" and a "collection" used to confuse me. That might be what OP wants to ask about. But if not, then that's true.
>>8109571
Crackpots sound friendly too, that doesn't make their bullshit any more useful.
>>8109571
>I read the prefaces and I feel like I got a personal student-teacher connection with the author
[math]\operatorname{Autism}~\operatorname{Detected}[/math]
>>8109559
>CS discrete math book detected
I don't even understand the author's argument. Can someone explain his reasoning?
>>8109779
No idea. Let me know if you figure out it.
>>8109779
I'm thinking the author meant to write (1,2,3), or [1,2,3], etc.
>>8109661
Rudin is fucking horrible time wise. The book is an introductory topology book and it seemed friendly enough to be a survey into the subject before I read a rigorous one but that one line was odd.
>>8109827
I love Rudin, but that's just me.
Anyway, for Topology, read Munkres.
His book is by far the best I've seen for introducing topology and it's also well-respected.
>>8110892
This. It's also surprisingly easy to self teach from Munkres (unlike Rudin).
>>8109827
I would recommend moving to a different book. Don't feel compelled to read the entirety of Munkres if that's what you decide to read, by the way.
>>8109827
"putting the objects within the second brackets"
I don't even know what "the second brackets" means.
