On: That's a Lot of YAML

[neilv]

That `AND:` being prefix-order was the hint it just needs a few small finishing touches:

  (select (num name)
     :from  customers
     :where (exists (select name
                       :from  orders
                       :where (and (= customers.num
                                      orders.customer_num)
                                   (< price 50)))))