Singular

LIB "chern.lib";
// Consider a 3-dimensional projective space
ring r = 0, (x, y, z, w), dp;
// Consider 3 non-coplanar lines trough one point and compute the Segre class
ideal I=xy, xz, yz;
I;
==> I[1]=xy
==> I[2]=xz
==> I[3]=yz
SegreA(I);
==> [1]:
==>    0
==> [2]:
==>    0
==> [3]:
==>    3
==> [4]:
==>    -10
// Now consider 3 coplanar lines trough one point and its Segre class
ideal J=w, x*y*(x+y);
J;
==> J[1]=w
==> J[2]=x2y+xy2
SegreA(J);
==> [1]:
==>    0
==> [2]:
==>    0
==> [3]:
==>    3
==> [4]:
==>    -12