FUNCTION: IsPe - test whether the argument is an element of the Pe-basis

CALLING SEQUENCE:

IsPe(expr)

TYP[IsPe](expr)

PARAMETERS:

expr = any expression

SYNOPSIS:

• The IsPe function tests whether expr is an element of the basis of products of elementary symmetric functions on a flag of alphabets. It is Pe[I] where I is a sequence of non-negative integers contained in the staircase [n, n-1, ..., 2, 1] in which n is the length of expr.

• The coding is such that we do not add a 0 at the end of the I's since it is implicit.

• Whenever there is a conflict between the function name IsPe and another name used in the same session, use the long form TYP['IsPe'].

EXAMPLES:

> with(TYP):
> IsPe(Pe[3,0,1]);
 
                                      true
 
> IsPe(Pe[3,0,2]);
 
                                     false