my $aant = (keys %HoHoA);
for (my $i = 1; $i<= $aant; $i++) {
     
    foreach my $keyA(sort keys %{$HoHoA{'set'.$i}}) {
         
        for (my $y = $i+1; $y<= $aant; $y++) {   
            foreach my $keyB(sort keys %{$HoHoA{'set'.$y}}) {
             
                print "$keyA - $keyB\n";
            } 
        }
    }
}

##</code><code>##

key1_set1 - key1_set2
key1_set1 - key2_set2
key1_set1 - key1_set3
key1_set1 - key2_set3
key1_set1 - key1_set4
key1_set1 - key2_set4
key1_set1 - key3_set4
key2_set1 - key1_set2
key2_set1 - key2_set2
key2_set1 - key1_set3
key2_set1 - key2_set3
key2_set1 - key1_set4
key2_set1 - key2_set4
key2_set1 - key3_set4
key1_set2 - key1_set3
key1_set2 - key2_set3
key1_set2 - key1_set4
key1_set2 - key2_set4
key1_set2 - key3_set4
key2_set2 - key1_set3
key2_set2 - key2_set3
key2_set2 - key1_set4
key2_set2 - key2_set4
key2_set2 - key3_set4
key1_set3 - key1_set4
key1_set3 - key2_set4
key1_set3 - key3_set4
key2_set3 - key1_set4
key2_set3 - key2_set4
key2_set3 - key3_set4