@a = split(//,$a);
@b = split(//,$b);
@c = split(//,$c);
foreach $a(@a){$test{$a}++}
foreach $b(@b){$test($b)++}
foreach $c(@c){$test($c)++)
foreach $test(keys %test){if($test{$test} eq 1){print "only one : $test\n"}}