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7.5.21.0. isInvertibleLeftFraction
Procedure from library olga.lib (see olga_lib).

Usage:
isInvertibleLeftFraction(frac, locType, locData), vector frac, int locType, list/vector/intvec locData

Purpose:
check if a fraction is invertible in the specified localization

Assume:

Return:
int

Note:
- returns 1, if the numerator of frac is in the denominator set, - returns 0, otherwise (NOTE: this does NOT mean that the fraction is not invertible, it just means it could not be determined by the method above).

Example:
 
LIB "olga.lib";
ring R = 0,(x,y,Dx,Dy),dp;
def S = Weyl();
setring S; S;
==> // coefficients: QQ
==> // number of vars : 4
==> //        block   1 : ordering dp
==> //                  : names    x y Dx Dy
==> //        block   2 : ordering C
==> // noncommutative relations:
==> //    Dxx=x*Dx+1
==> //    Dyy=y*Dy+1
poly g1 = x+3;
poly g2 = x*y;
list L = g1,g2;
vector frac = [g1*g2, 17, 0, 0];
isInvertibleLeftFraction(frac, 0, L);
==> 1
ideal p = x-1, y;
frac = [g1, x, 0, 0];
isInvertibleLeftFraction(frac, 1, p);
==> 1
intvec rat = 1,2;
frac = [g1*g2, Dx, 0, 0];
isInvertibleLeftFraction(frac, 2, rat);
==> 0


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