Operation: Issue a Book (continued)
shelved ? dom issued = dom stock
shelved' ? dom issued' = dom stock'
shelved ? dom issued = Ø; shelved' ? dom issued' = Ø
ran issued ? readers; ran issued' ? readers'
?r : readers ? #(issued ? {r}) maxloans
?r : readers' ? #(issued' ? {r}) maxloans
c? ? shelved; r? ? readers; #(issued ? {r?}) < maxloans
issued' = issued ? {c? r?}
stock' = stock; readers' = readers