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

CALLING SEQUENCE:

IsY(expr)

TYP[IsY](expr)

PARAMETERS:

expr = any expression

SYNOPSIS:

• The IsY function tests whether expr is a 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 IsY and another name used in the same session, use the long form TYP['IsY'].

EXAMPLES:

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