FUNCTION: mchpg - test an algebra for being of polynomial growth

CALLING SEQUENCE:
mchpg(a)
mchpg(a,s,p,m,c,incl,img)

PARAMETERS:
a - a completely separating bound poset algebra
s, p, m, c, incl, img - optional arguments evaluating to names

SYNOPSIS:

• mchpg tests whether its first argument, the bound poset algebra a, is of polynomial growth.

• For mchpg to work properly, the algebra a has to be completely separating.

• Testing is done by constructing for each point s of the algebra the poset of minimal chain sequences starting in s and then looking first for minimal wild (or hypercritical) subposets there, and then for a minimal tame subposet.

  If the algebra is not of polynomial growth, various data will be returned through the optional arguments. In particular:
  
  s - will be a point for which there is a poset of minimal chain sequences that is not of polynomial growth.
  
  p - will contain the poset structure of the poset belonging to s.
  
  m - a table containing for each minimal chain sequence in p the corresponding s-start set.
  
  c - will give the name of the hypercritical subposet or of the minimal tame non polynomial growth subposet of p found by the function.
  
  incl - a list containing data about the inclusion c --> p found by the function. In fact incl[i] is the image in p of the point i of c under this inclusion.
  
  img - a vector marking the points of p belonging to the image of c by 1, those not belonging to the image by 0.