isStandard -- test whether a Filling is semistandard

• Usage:

  isStandard T

• Inputs:
  • T, an instance of the type Filling, assumed to have strictly increasing columns (for example, the output of normalize); the routine scans adjacent columns right to left for the first row-ascent violation
• Outputs:
  • null if T is semistandard (entries weakly increase along every row), otherwise a pair (i, j) such that T#i#j > T#(i+1)#j

i1 : isStandard new Filling from {{0,1}, {1,2}}

i2 : isStandard new Filling from {{1,2}, {0,1}}

o2 = (0, 0)

o2 : Sequence