| LIB "algebra.lib";
ring r = 0,(a,b,c),ds;
ring s = 0,(x,y,z,u,v,w),dp;
ideal I = x-w,u2w+1,yz-v;
map phi = r,I; // a map from r to s:
alg_kernel(phi,r); // a,b,c ---> x-w,u2w+1,yz-v
→ 0
ring S = 0,(a,b,c),ds;
ring R = 0,(x,y,z),dp;
qring Q = std(x-y);
ideal i = x, y, x2-y3;
map phi = S,i; // a map to a quotient ring
alg_kernel(phi,S,"ker",3); // uses algorithm 3
→ a-b,b^3-b^2+c
setring S; // you have access to kernel in preimage
ker;
→ ker[1]=a-b
→ ker[2]=c-b2+b3
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