[fzhfzh]

mgx-alander wrote:

wtf still cannot use exchange.nus.edu.sg

simi lan jiao

fark la

I very dulan with outlook already... just because NUS email down and it cannot access it, it won't even startup for my other email accounts...

[yoshi_fanboy]

Death4ngel wrote:

How to prove

Proposition 6. The set Z is countably infinite.

Proposition 8. The set Q is countably infinite.

Am I suppose to explicitly define the function? What if I am not supposed to?

As far as I know of, for the set of integers, I can't think of a way to prove that the set of integers is countably infinite, without explicitly defining a bijection between the set of natural numbers and the set of integers.

However, for the rational numbers, you could show that there is an injection from the set of rational numbers Q to the set ZxZ. Then ZxZ is equipotent to NxN, which in turn is equipotent to N itself. To show the last statement, consider the function f: NxN -> N, given by f(m,n)=(m+n-2)(m+n-1)/2+m.
Then f is a bijection. So there exists an injection from Q to N, so Q is countably infinite.

So in one way or another, you do need to define a bijection from N to Q, or an injection from Q to N, or a surjection from N to Q somehow.

[yoshi_fanboy]

Anyway, MA2108S is not a course on set theory, so you do not need to worry about that lol.

[mgx-alander]

fzhfzh wrote:

I very dulan with outlook already... just because NUS email down and it cannot access it, it won't even startup for my other email accounts...

fark microsoft

[SoriyaGTR34]

tmd, the website give me false hope that can login to nus mail...end up also cannot...

[SoriyaGTR34]

eh people, can use liao...

[nomnomnom]

up and running!

[tehhalia]

heng smooth liao,
if not cannot summit report then die

[nomnomnom]

Anyone taking special sem? Want take with me?

[Death4ngel]

yoshi_fanboy wrote:

Anyway, MA2108S is not a course on set theory, so you do not need to worry about that lol.

Later mid terms come out sets and counting then hong gan sia!

[napsterz]

nomnomnom wrote:

Anyone taking special sem? Want take with me?

you sponsor ?

[napsterz]

what is MIT ?

[fzhfzh]

amuletheart wrote:

MIT >.< so lucky. Jealous.

It's not luck, it's 実力.

[fzhfzh]

sian, BRDF equation makes my head spin...

[mgx-alander]

greenspeak wrote:

moi ma1312 mid-term get 30+ nia

Moi MA1521 mid term last sem i got 34