I've said it before, but slot-controlled or gate-controlled airports should put the slots and gates up for bid on a regular basis. There is no reason that WN should have a monopoly at DAL (or DL should have slots at JFK) simply due to first-mover advantage. If the asset is valuable, and clearly it is if UA is leasing them, then put them up for auction and let the public benefit. There is no reason UA should benefit from something they won't use.