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my @A = (1,2,3,4,5,4,3,2,1,2);
my @B = (2,4,6,8,10,8,6,4,2);
...
for (sort keys %Pairs){
  print "$_:\n", map("  $_\n", map(join('-', @$_), @{ $Pairs{$_} })), 
+"\n";
}

push @{ $First{  $A[$_] } }, $_ for (0..$#A);
push @{ $Second{ $B[$_] } }, $_ for (0..$#B);

  for my $Common (grep {exists $Second{$_}} keys %First){

  for my $Idx (@{ $First{$Common} }){
    push @{ $Pairs{$Common} }, map([$Idx, $_], @{ $Second{$Common} });
  }

  $Pairs{Each Common Value} = [ [A1, B1], [A1, B2], [A2, B1], [A2, B2]
+ ]

  $Pairs{4} = [[3,1], [3,7], [5,1], [5,7]]

2:
  1-0
...
  3-7
  5-1
  5-7