Programming Ruby 3.2 (5th Edition): B1.0 page 248, missing are?

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@noelrappin

page 248, second paragraph after the first code, line 3 : missing are ???

you to set up two special variables called CLEAN and CLOBBER, which initially an empty list
                                                                      -----> ^ <----- are ?

Should be : which initially are an empty list

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Thanks!