DB<154> @a0 =  (-20,20,1,1,2,2,2,9,3,-4,-4,5,-20,20);
 => (-20, 20, 1, 1, 2, 2, 2, 9, 3, -4, -4, 5, -20, 20)

  DB<155> @a1 = ( 10,11,7,9,3,3,3,1,3, 4, 5,5,  1,30); 
 => (10, 11, 7, 9, 3, 3, 3, 1, 3, 4, 5, 5, 1, 30)

  DB<156> map { push @{$group{$a0[$_]}},$a1[$_] } 0..$#a0

  DB<157> sub highlander { 
             my @sort = sort @{ shift() } ; 
             return $sort[-1]>$sort[0] ? $sort[-1] : undef 
          } 

  DB<158> @high{keys %group } = map { highlander($_) } values %group 
=> (undef, 5, undef, undef, 30, 9, 10, undef)

  DB<159> map { ($a0[$_],$a1[$_])=() if $a1[$_] != $high{ $a0[$_] } } 0..$#a0 

  DB<160> \@a0
 => [
  -20,
  undef,
  undef,
  1,
  undef,
  undef,
  undef,
  undef,
  undef,
  undef,
  -4,
  undef,
  undef,
  20,
]

  DB<161> \@a1
 => [
  10,
  undef,
  undef,
  9,
  undef,
  undef,
  undef,
  undef,
  undef,
  undef,
  5,
  undef,
  undef,
  30,
]