#         @a      @b        @a       @b
  # same?  range   range    values   values
  (   0,   0=>0,   0=>-1,  #    a  !
      1,   1=>2,   0=> 1,  #  b c  =  b c
      0,   3=>2,   2=> 2,  #       !  d
      1,   3=>3,   3=> 3,  #    e  =  e
      0,   4=>4,   4=> 4,  #    f  !  h
      1,   5=>5,   5=> 5,  #    j  =  j
      0,   6=>5,   6=> 6,  #       !  k
      1,   6=>7,   7=> 8,  #  l m  =  l m
      0,   8=>9,   9=>11,  #  n p  !  r s t
  );