FUNCTION: pspg - test a poset for polynomial growth

CALLING SEQUENCE:
pspg(p)
pspg(p,c,incl,img)

PARAMETERS:
p - a poset
c, incl, img - optional arguments evaluating to names

SYNOPSIS:

• pspg tests, whether the poset p is of polynomial growth.

• Testing is done by first looking for hypercritical subposets and then for a minimal non-polynomial growth subposet. (Criterion of Zavadskij)

• If the poset is not of polynomial growth, various data will be returned via the optional arguments. In particular:
  
  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.

EXAMPLES:

> p:= [7,{[1, 2, 3], [3, 4, 5], [2, 4, 5]}];

> pspg(p,'c','incl','img');

> print(c);

> print(incl);

> print(img);