FUNCTION: IsSkewDiag - test whether the argument is a skew diagram

CALLING SEQUENCE:

IsSkewDiag(expr)

TYP[IsSkewDiag](expr)

PARAMETERS:

expr = any expression

SYNOPSIS:

• The IsSkewDiag function tests whether expr is a skew diagram, that is, a list with two components l1 and l2, l1 being the exterior shape, l2 the interior shape. The diagram must be without empty rows, nor columns (equivalently, l1[i] >= l2[i-1] for all i).

• Skew diagrams are special cases of skew partitions.

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

EXAMPLES:

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