divisors.lib
LIB "divisors.lib"; ring r=31991,(x,y,z),dp; ideal I = y^2*z - x*(x-z)*(x+3*z); qring Q = std(I); divisor A = makeDivisor(ideal(x,z),ideal(1)); divisor B = makeDivisor(ideal(x,y),ideal(1)); divisor D = divisorplus(multdivisor(2,B),negativedivisor(A)); effective(D); ==> (z,x) - (1) ==>