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7.5.21.0. isInvertibleNcfrac
Procedure from library ncfrac.lib (see ncfrac_lib).

Usage:
isInvertibleNcfrac(frac), ncfrac frac

Purpose:
checks if frac is invertible

Return:
int, 1 if frac is invertible, 0 otherwise

Example:
 
LIB "ncfrac.lib";
==> // ** redefining testNcfrac (LIB "ncfrac.lib";)
==> // ** redefining testNcloc (    LIB "ncloc.lib";)
ring R = 0,(x,y,Dx,Dy),dp;
def S = Weyl();
setring S;
ncloc loc = intvec(2);
ncfrac frac = list([y,y+1,0,0], loc);
isInvertibleNcfrac(frac);
==> 1
frac = list([y,x+1,0,0], loc);
isInvertibleNcfrac(frac);
==> 0