Use R ::= QQ[x,y,z];
X1 := [[0,0,1],[1,0,1],[2,0,1],[2,1,1]]; -- 4 points in the projective
-- plane
X2 := [[0,0,1],[1,0,1],[0,1,1],[1,1,1]]; -- 4 more points
I1 := IdealOfProjectivePoints(X1);
I2 := IdealOfProjectivePoints(X2);
Hilbert(R/I1); -- the Hilbert function of X1
H(0) = 1
H(1) = 3
H(x) = 4 for t >= 2
-------------------------------
Hilbert(R/I2) = Hilbert(R/I1); -- The Hilbert functions for X1 and X2
-- are the same
TRUE
-------------------------------
Res(R/I1); -- but the resolutions ...
0 --> R(-3)(+)R(-4) --> R^2(-2)(+)R(-3) --> R
-------------------------------
Res(R/I2); -- are different.
0 --> R(-4) --> R^2(-2) --> R
-------------------------------
Describe Res(R/I1); -- more information about the resolution for X1
Mat([
[xy - 2yz, y^2 - yz, x^3 - 3x^2z + 2xz^2]
])
Mat([
[y - z, x^2 - xz],
[-x + 2z, 0],
[0, -y]
])
-------------------------------
Syz(I1,1); -- the first syzygy module for X1
Module([y - z, -x + 2z, 0], [x^2 - xz, 0, -y])
-------------------------------
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