Add ", at" before the page

Error²Federal courts, Illinois courts21st and 22nd editions

Where a work's title ends in a numeral, the page is set off by a comma and “at”, so the number does not read as part of the title.¹

1. 1R. 15.3 Title; R. 3.2(a) Pages.
2. 2An error: the rule in note 1 allows one form, and this is not it.