[GAP Forum] Serious bug in `PolynomialReduction'

[Alexander Hulpke]

Dear GAP Forum,

A user has reported a serious bug in the code for polynomial  
reduction (thus also affecting Groebner bases), which may return  
wrong results without warning. (See below for an example)
This bug will be corrected in the forthcoming next bugfix.

If you are using Groebner bases and need a temporary workaround  
already now, you can
download the file
http://www.math.colostate.edu/~hulpke/workaround.gi
Read this file in with *Reread* (not Read, as it overwrites some  
library functions)

We apologize for this problem!

    Alexander Hulpke

Example with correct output:
x:=X(Rationals,"x");;
y:=X(Rationals,"y");;
a:=X(Rationals,"a");;
c:=X(Rationals,"c");;
s:=X(Rationals,"s");;
L:=[(a+c)*s-x,(a+c)*c-y,s^2+c^2-1];;
ReducedGroebnerBasis(L,MonomialLexOrdering([x,y,a,c,s]));
[ c^2+s^2-1, -a*c+s^2+y-1, -a*s-c*s+x ]
(2nd polynomial was wrong!)

-- Colorado State University, Department of Mathematics,
Weber Building, 1874 Campus Delivery, Fort Collins, CO 80523-1874, USA
email: hulpke at math.colostate.edu, Phone: ++1-970-4914288
http://www.math.colostate.edu/~hulpke