X
f:X→⋃Y∈XY
Y∈X
Y
f
f(Y)∈Y
∀X([∀Y∈XY≠∅]⇒[∃(f:X→⋃Y∈XY)(∀Y∈X∃y∈Yf(Y)=y)])
Y1,Y2,Y3
y1∈Y1,y2∈Y2,y3∈Y3
f(Y1)=y1
f(Y2)=y2
f(Y3)=y3
Y1,Y2,Y3,…
n
ax2+bx+c=0
−∞
+∞,
0
1
P(X)+P(¬X)
¬X
ℵ0
{+,˙,0,1}
26=64
p<0.05
10betthatpaidout
8
4
log48
1.5
3
2
log23
n∈R≥1,
∈R≥0
f(xy)=yf(x)
f(bn)=nf(b)
f(b)=1⟹f(bn)=n,
(R>0,⋅)
(R,+)
log
R
s(d)=surprise(d∣H)=−logPr
$~$x, y, z$~$