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a b c
0 0 d
0 1 d
...
1 1 d
1 2 d
1 2 d

a b c    a b c    
0 0 d    1 0 d
0 1 d    1 0 d
0 1 d    1 1 d
0 2 d    1 2 d
0 2 d    1 2 d

foreach my $va (sort {$a <=> $b} keys %myhash) {
           foreach my $vb (sort {$a <=> $b} keys %{ $myhash{$va} }) {
                   my $vc = $myhash{$va}{$vb};
...
            }
        }
}