Rent ceiling on a fixed housing stock: the cap cannot add apartments, so it opens a shortage and pushes competition into queues and favors S E2 E1 P2 P1 Monthly rent ($) Apartments Ceiling: $4.0 Da+D′b Da+Db Value competed away in queues and favors Qs = 5 (the stock) Qd = 8 F G Shortage Ceiling at $4.0 → renters want 8 units; only 5 exist (Qd 8 vs Qs 5). The cap can’t add apartments — it opens a 3-unit shortage, and the full rent — money plus queues and favors — climbs toward the $7.0 clearing rent. Drag the ceiling up or down — or tab to it and use the arrow keys.