FUNCTION: IsX - test whether the argument is a Schubert polynomial

CALLING SEQUENCE:

IsX(expr)

TYP[IsX](expr)

PARAMETERS:

expr = any expression

SYNOPSIS:

• The IsX function tests whether expr is a Schubert polynomial indexed by a permutation.

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

EXAMPLES:

> with(TYP):
> IsX(X[3,1]);
 
                                false
 
> IsX(X[3,1,2]);
 
                                 true