Question: On January 5, AA Crystal, an importer of fine glass ware, conveyed to Chester a letter offering to sell 100 imported crystal wine glasses for $170 per glass. The letter indicated that the offer would remain in effect for 20 days. On January 9, there was an unexpected increase in the price of crystal glassware, and AA Crystal sent a letter to Chester formally withdrawing the offer to sell. Chester received the revocation of the offer on January 11. On January 21, Chester mailed a letter accepting to the original offer to sell to him 100 imported glasses. The letter was received by the seller on January 27. Please explain whether a valid sale took place in this case or not.