Damn, you're right... sorry :-)

Brian Candler wrote:
> Mark Kremer wrote:
>   
>> I'm not sure if you still want the regex, but following regex should do
>> the trick: ^(.{1})(?!\1)(.{1})(?!\1|\2).{1}\2$
>>     
>
> Which is the same as the one I posted in my initial reply:
>
> irb(main):009:0> /^(.)(?!\1)(.)(?!\1|\2)(.)(\2)$/ =~ "abcb"
> => 0
> irb(main):010:0> /^(.)(?!\1)(.)(?!\1|\2)(.)(\2)$/ =~ "abbb"
> => nil
>