/*================( Quick sort at position )================*/
QSortAtPos: Procedure Expose stem.
Arg left, right, sPos, sLen

If Datatype( fromX, "NUM" ) = 0 | fromX < 1 Then fromX = 1
If Datatype( toX, "NUM" ) = 0 | toX > stem.0 Then toX = stem.0

If right > left Then Do
  i = left
  j = right
  k = (left+right)%2
  
  If DataType( sPos, 'NUM' ) = 0 ! sPos < 1 Then sPos = 1
  If DataType( sLen, 'NUM' ) = 0 ! sLen < 1 Then sLen = Length( stem.k ) - sPos + 1
  x = Substr( stem.k, sPos, sLen )
  Do Until i > j
    Do While Substr( stem.i, sPos, sLen ) << x; i = i + 1; End
    Do While Substr( stem.j, sPos, sLen ) >> x; j = j - 1; End
    If i <= j Then Do
      xchg = stem.i
      stem.i = stem.j
      stem.j = xchg
      i = i + 1
      j = j - 1
    End
  End
  y = QSort( left, j, sPos, sLen )
  y = QSort( i,right, sPos, sLen )
End

Return right - left
/*** End QSortAtPos ***/