FUNCTION: IsXX - test whether the argument is a double Schubert polynomial

CALLING SEQUENCE:

IsXX(expr)

TYP[IsXX](expr)

PARAMETERS:

expr = any expression

SYNOPSIS:

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

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

EXAMPLES:

> with(TYP):
> IsXX(XX[3,1]);
 
                                false
 
> IsXX(XX[3,1,2]);
 
                                 true