|  |  D.15.13.13 formaldivisorplus Procedure from librarydivisors.lib(see  divisors_lib).
 
Example:Usage:
formaldivisorplus(A ,B); A + B; A = formaldivisor, B = formaldivisor. 
 
Assume:
A and B are formal divisors on X.
Return:
a formal divisor on X
Theory:
The procedure will add the formal sums.
 |  | LIB "divisors.lib";
==> Welcome to polymake version
==> Copyright (c) 1997-2015
==> Ewgenij Gawrilow, Michael Joswig (TU Darmstadt)
==> http://www.polymake.org
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 C = makeDivisor(ideal(x-z,y),ideal(1));
formaldivisor fE= makeFormalDivisor(list(list(-5,A),list(2,B)));
formaldivisor fE2= makeFormalDivisor(list(list(-5,A),list(2,C)));
formaldivisorplus(fE,fE2);
==> [1]:
==>    [1]:
==>       -10
==>    [2]:
==>       (z,x) - (1)
==> 
==> [2]:
==>    [1]:
==>       2
==>    [2]:
==>       (y,x) - (1)
==> 
==> [3]:
==>    [1]:
==>       2
==>    [2]:
==>       (y,x-z) - (1)
==> 
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