Congrats for making me go look up x= ("Get outta here, that's legal? So it is!")

For Perl historians, note that the "$_ x= boolean expression" idiom is attributed to Larry Wall in the early 1990s. IIRC, this attribution was made by japhy around the time of the first fwp golf games in 2001, for example it is mentioned in this post and elsewhere.

Also of interest for Perl golf historians is that, as indicated in mtve's golf history book (page 36), Eugene van der Pijll won the second ever fwp golf game, "Get Even", in 2002, by employing Larry's concoction:

-p $_ x=1&~$.&split$&while aeiouy=~/.?/g
[download]

to solve a similar problem to this game, namely printing all words in a dictionary that satisfy the following constraints: i) are on an even line in the words file; ii) have an even word length; iii) contain an even number of each and every vowel.

BTW, this game produced some very funny looking solutions, such as this one by Sean McAfee (which, if you squint, you will notice uses Abigail's length horror y///c):

-ln 1&($.|y|||c|y|a|||y|e|||y|i|||y|o|||y|u|||y|y||)||print
[download]