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

CALLING SEQUENCE:

IsYY(expr)

TYP[IsYY](expr)

PARAMETERS:

expr = any expression

SYNOPSIS:

• The IsYY function tests whether expr is a double Schubert polynomial indexed by a sequence of non-negative integers (interpreted as the code of a permutation).

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

EXAMPLES:

> with(TYP):
> IsYY(YY[0,1,2,0]);
 
                                 true
 
> IsYY(YY[0,-1]);
 
                                 false