|  |  D.5.4.2 divisorplus Procedure from librarydivisors.lib(see  divisors_lib).
 
Example:Usage:
divisorplus(A ,B); A + B; A = divisor, B = divisor. 
 
Assume:
A and B are divisors on X.
Return:
a divisor on X
Theory:
The procedure will compute the product of the numerator
and denominator ideals, respectively.
 |  | 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));
A+B;
==> (x,yz) - (1)
==> 
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