The owner of an art gallery entered into a written contract with an avid art collector whereby the art collector agreed to buy and the gallery owner agreed to sell for $7,500 any painting in the gallery by artist alpha. the contract was to be executed on july 6 according to its written terms. the art collector went to the gallery on july 6 with a certified check in the amount of $7,500. the art collector pointed out a painting by a different artist hanging on the wall, and told the gallery owner that that was the painting he wanted, and that he would also take its old-fashioned $250 gilt frame to go with it. the gallery owner responded that the painting was by the artist beta, but that the art collector could have it with the frame if he was willing to pay $250 extra for it. this enraged the art collector, and he filed suit against the gallery owner, asserting in his pleading that he remains able and willing to tender $7,500 to the gallery owner. he also asserts that prior to signing the contract, the parties agreed orally that the art collector could have a painting by beta for the same price in lieu of one by alpha, and that the gallery owner would throw in the frame for whatever painting he chose. the gallery owner denied that any such conversation took place. there are no other witnesses. about which agreements should the court allow the art collector to testify?