Algèbre et géométrie II Série 4

X X+X
R, B1(0) = {x∈R2||x|<1}, B1(0) = {x∈R2||x| ≤ 1}.
U⊂X+X
U X
U=X+−C C ⊂X
X+
X1, X2Y X1X2
X1×X2X1X2
X1×X2X1X2
f:Y−→ X1×X2
f1:Y−→ X1f2:Y−→ X2
f:X→Y
f Y
Gf:= {(x, f(x)) ∈X×Y|x∈X}
X×Y
GfY f
Y={p, q} O ={∅, Y }N>0={1,2,3, . . .}
X:= Y×N>0
A⊂X

Z
a∈N\ {0}b∈Z
Za,b =an +b:n∈Z⊂Z.
T ∅ Za,b
Z
∅
P P ={p1, . . . , pr}
Z\ {−1,1}Zpi,bi