A quantum leap in electricity pricing theory occurred in 1988 when four professors at MIT and Boston University (Fred C. Schweppe, Michael C. Caramanis, Richard D. Tabors, and Roger E. Bohn) published a book entitled, "Spot Pricing of Electricity". It presented the concept that prices at each location on a transmission system should reflect the marginal cost of serving one additional unit of demand at that location. It then proposed quantifying these prices by solving a systemwide cost minimization problem while complying with all of the system's operational constraints, such as generator capacity limits, locational loads, line flow limits, etc. using linear programming software. The locational marginal prices then emerged as the shadow prices for relaxing the load limit at each location.