 economic event with another economic event, which should be recorded with a <code>corrects</code> link to the original event.  This gives flexibility to display the event as corrected, or as separate events, depending on the need.  The quantity should be the amount to be added or subtracted from the original event quantity.  So this works differently than the increment/decrement rules, and will be the only time negative quantities can be used.  It is not required, but is often customary to completely "back