# Singular

##### 7.5.23.0. 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 ```