/Perl M(?:(o)|(u))n(?(2)(g)|(?:(g)|(k)))(?(5)|er)s/; Only one extra 'g' wasted? What about the two occurences of 'er'?! As one of the most common digrams in the English language; we need to conserve it as much as possible! /P(er)l M(?:(o)|(u))n(?(3)(g)|(?:(g)|(k)))(?(6)|\1)s/; :)