imagine sort of two unconstrained systems one in which as a passenger whenever I request a ride there's always a driver waiting for me all right and another in which as a driver whenever I finish driving there's always a passenger right there requesting a ride that I can get matched to okay so in one of them demand is not a canoe in the first system I just described supply is not a constraint the second one demand is not a constraint so each of these two sort of naturally give you a supply curve in a demand curve this expression