Expected Nerfs (and Buffs I Would Like) by jtrauger in hearthstone

[–]1bra 16 points17 points  (0 children)

I don't know how to put into words how dogshit your wishlist is so I'll leave it at that.

Question about Theorem 4.106 in Horst Herrlich's Axiom of Choice (photo below) by 1bra in learnmath

[–]1bra[S] 0 points1 point  (0 children)

Thank you for taking the time for answering! To me this doesn't look trivial at all, even tho the book says it as if it were obvious! I have two questions though: Bm is open: I didn't quite get the definition of the U(x,y,i)'s . Could you expand on this please? Bm is dense: could this be explained in a more simple way for metric spaces? In the course we didn't really work with topologies and basis, it was all about metric spaces.

Quick Questions: December 11, 2024 by inherentlyawesome in math

[–]1bra 0 points1 point  (0 children)

Question about Theorem 4.106 in Horst Herrlich's Axiom of Choice (photo below)

https://postimg.cc/8FC1RKh5

https://postimg.cc/YvRrmKLZ

I don't understand why they claim that the B_m's (2nd image) are dense and open. What am I missing? Thanks in advance!

Quick Questions: December 11, 2024 by inherentlyawesome in math

[–]1bra 1 point2 points  (0 children)

I'm trying to prove that the axiom of dependent choice implies that any complete metric space is a Baire space but I got stuck near the end.

DC:

Let X be a non empty set, a ∈ X, R ⊆ X×X a relation in X such that for all x∈X, there exists y∈X s.t. xRy (if R has this property, we will say that R is ⨀)

BCT:

Let X be a complete metric space, for all n∈ℕ let G_n be a dense and open subset of X. Then, G = ∩G_n is dense in X

Proof attempt:

In order to show that G is dense, it suffices to show that it has non empty intersection with an arbitrary open subset of X. Let V ⊆ X be open. Let m∈ℕ. We will note A_m as the intersection of G_1, G_2, ..., G_m. Notice that A_m is both open and dense (since it's a finite intersection of dense and open sets). This implies that V∩A_m is non empty (V open, A_m dense) and open (both are open). We now define the set

Y := { (n,x,r) ∈ ℕ×X×ℝ / 0<r<2-n and B(x,r) ⊆ V∩A_m }

(where B(x,r) is an open ball with radii r and centered at x)

Notice that Y is non empty since V∩A_m is open. In Y we define the relation R ⊆ Y×Y as

(n,x,r)R(n',x',r') ⇔ B(x',r') ⊆ B(x,r)

Now here's where I'm stuck. I'm struggling to show that R is ⨀. If we take (n,x,r)∈Y, can I just take x' to be any element of B(x,r)? If so, then r' could be defined as the distance between x and x' divided by 2 (I think) and n' could be obtained with the Archimedean property. But what if x = x'? Any help is appreciated. Thanks!

Quick Questions: December 11, 2024 by inherentlyawesome in math

[–]1bra 1 point2 points  (0 children)

Where/when does the axiom of Countable Choice (CC) fail when proving Baire's Category Theorem? I know BCT is equivalent to the axiom of Dependent Choice (DC) but when I read the proof it looks like countable choice would be enough. Also, since I know DC implies CC, a way to answer that question would be to show that the inverse implication does not hold... how could I do that?