In a writing signed by both parties on December 1, Kranc agreed to buy from Schaff a gasoline engine for $1,000, delivery to be made on the following for $1,000, delivery to be made on the following February 1. Through a secretarial error, the writing called for delivery on March 1, but neither party noticed the error until February 1. Before signing the agreement, Kranc and Schaff orally agreed that the contract of sale would be effective only if Kranc should notify Schaff in writing not later than January 2 that Kranc had arranged to resell the engine to a third person. Otherwise, they agreed orally, "There is no deal." On December 15, Kranc entered into a contract with Trimota to resell the engine to Trimota at a profit. For this question only, assume the following facts. Kranc did not give Schaff notice of the resale until January 25, and Schaff received it by mail on January 26. Meantime, the value of the engine had unexpectedly increased about 75% since December 1, and Schaff renounced the agreement. If Kranc sues Schaff on February 2 for breach of contract, which of the following is Schaff's best defense? 
The secretarial error in the written delivery-term was a mutual mistake concerning a basic fact, and the concerning a basic fact, and the agreement is voidable by either party.  Kranc's not giving written notice by January 2 of his resale was a failure of a condition precedent to the existence of a contract. In view of the unexpected 75% increase in value of the engine after December 1, Schaff's performance is excused by the doctrine of commercial frustration.  The agreement, if any, is unenforceable because a material term was not included in the writing. 