alias rot13 [
	push alpha [
		"A B C D E F G H I J K L M N O P Q R S T U V W X Y Z"
		"a b c d e f g h i j k l m n o p q r s t u v w x y z"
	] [ push chars [] [
		loop i (strlen $arg1) [
			looplist n $alpha [
				if (! (listlen $chars)) [
					alias chars (? (> (listindex $n (substr $arg1 $i 1)) -1) $n [])
				]
			]
			alias arg1 (
				concatword (substr $arg1 0 $i) (
					? (listlen $chars) (
						at $chars (
							mod (+ (
								listindex $chars (substr $arg1 $i 1)
							) 13 ) (listlen $chars)
						)
					) (substr $arg1 $i 1)
				) (substr $arg1 (+ $i 1) (strlen $arg1))
			)
			alias chars []
		]
	] ]
	result $arg1
]