In 1968, P and NASA were both leasing space at an office building owned by the Wyman Street Trust. NASA decided to expand its footage, and at the same time P was seeking to move to larger quarters in another location. The United States (D) reached an agreement as to NASA's rental of P's 2,093 square foot computer room on the first floor. P would surrender possession of the computer room, and D would lease it (from Wyman). D promised to pay Wyman $39,000 for air conditioning equipment which P had installed in the computer room, and Wyman obliged itself in the same amount in payment to P. P had not vacated by January 1, 1969 (the agreed upon date), and on the next day D sent P a letter informing it that D canceled the lease because it was not available for occupancy on January 1, 1969. Wyman Street Trust refused to take action to collect the $39,000 from D and eventually Wyman assigned its rights to the $39,000 under the lease amendment to D. P sued D place of Wyman. P argued the American Rule wherein Wyman had fully performed its duty as a landlord because Wyman was only obligated to convey the right to possession to the room and not actual possession. D argued the English Rule.