K
K[x1, . . . , xn]K[x0, . . . , xn]
R K[x1, . . . , xn]
K[x0, . . . , xn]
n n K
An(K)An
S⊂K[x1, . . . , xn]
V(S) = x∈Kn:f(x)=0,∀f∈S⊂An.
V
I, I0, J ⊂K[x1, . . . , xn]I⊂I0S, S0⊂K[x1, . . . , xn]
V(I)⊃ V(I0)
V(S) = V(hSi)
V(IJ) = V(I)∪ V(J) = V(I∩J)
V(S∪S0) = V(S)∩ V(S0)
V(I+J) = V(I)∩ V(J)
(i)
(ii)V(hSi)⊂ V(S)
x∈ V(S)g∈ hSig1, . . . , gm∈S
f1, . . . , fmK[x1, . . . , xn]
g=
m
X
i=1
gifi.