Mistake (contract law) void. Traditionally, Caveat Emptor (let the buyer beware), and under Common Law Caveat Venditor (let the seller beware). A contract might be voidable from unilateral mistake for any of the following: A mutual mistake occurs when the parties to a contract are both mistaken about the same "material" fact within their contract. They are at cross-purposes. There is a meeting of the minds, but the parties are mistaken. Hence the contract is voidable. "Collateral" mistakes will not afford the right of rescission. A collateral mistake is one that 'does not go to the heart' of the contract. For a mutual
Patent caveat as the proposed patent, the Patent Office notified the holder of the caveat, who then had three months to submit a formal patent application with claims. If the two patent applications claimed the same invention, an interference would then be declared and neither patent could be issued until it was determined which was the first to invent. Perhaps the most famous example of such a conflict was on 14 February 1876, when Elisha Gray filed a patent caveat and Alexander Graham Bell filed a patent application on the same day, both relating to the telephone. Gray ended up abandoning his