On 1s' February 2022, William wrote a letter to Roy offering to sell his cat, Comel, at the price of RM2000. William gave Roy until 10th February to accept his offer. Roy received the letter on 3rd February 2022 and posted a letter, accepting William's offer on 9th February 2022. William, however, has changed his mind about selling Comel. He posted a letter to Roy on 7' February 2022 revoking his offer. Roy received the letter of revocation on 10t February 2022, and William received Roy's letter of acceptance on 12th February 2022. Advise Roy on whether a contract has been constituted. Support your answers with all relevant authorities, including case law, provisions of the statutes, and others.