Outlook calendar invites use s-expressions to describe the rules for when a recurring event is scheduled. Lisp lives in the most unexpected places.
(and (not (diary-date 5 1 2015)) (diary-cyclic 7 4 10 2015) (diary-block 4 10 2015 7 31 2015))
(and (not (diary-date 5 1 2015)) (diary-cyclic 7 4 10 2015) (diary-block 4 10 2015 7 31 2015))
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