my $re = qr[
	(.) (?=(.)(.))
	(?= .* 
		(?: 
			\1 (?: \2\3 | \3\2 ) 
			| 
			\2 (?: \1\3 | \3\1 )
			| 
			\3 (?: \1\2 | \2\1 )
		)
	.* $)
]x;