Ralph wants to sell his house, as is (meaning, “no warrantie…

Ralph wants to sell his house, as is (meaning, “no warranties”), for $395,000. His neighbor, Juan, expresses interest in buying the house but wants time to think it over. Juan asks Ralph to keep the offer open for five days. Ralph gives Juan a written document, without a signature, that states, “Ralph will not revoke the offer for five days.” Three days later, Ralph revokes the offer. Juan argues the offer was not revocable for another two days. Was the offer revocable?