Procedure from library mondromy.lib (see mondromy_lib).
mondromy.lib
invunit(u,n); u poly, n int
The polynomial u is a series unit.
The procedure returns the series inverse of u up to order n or a zero polynomial if u is no series unit.
The procedure displays comments if printlevel>=1.
Example:
LIB "mondromy.lib"; ring R=0,(x,y),dp; invunit(2+x3+xy4,10); → 1/8x2y8-1/16x9+1/4x4y4+1/8x6-1/4xy4-1/4x3+1/2