Is the second example not a set because it's not denoted

>>8109559
time to find a new textbook

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>>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.

>>8109559
That's truly, truly bizarre.

>>8109565
I echo this person's sentiment.

>>8109571
Sorre OHPEE but >>8109565 is right
That shit from your book makes as much sense as saying that dog is a verb and not a noun so it should never be used as a noun

>>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.

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>>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.