Consider the crossword puzzle shown in the below figure. A1,D1 D2 D3 A2 ETT A3 Word list: add, ado, age, ago, aid, ail, aim, air, and, any, ape, apt, arc, are, ark, arm, art, ash, ask, auk, awe, awl, aye, bad, bag, ban, bat, bee, boa, ear, eel, eft, far, fat, fit, lee, oaf, rat, tar, tie. You must find six three-letter words: three words read across (A1, A2, and A3) and three words read down (D1, D2, and D3). Each word must be chosen from the list of forty possible words shown. Build a set of constraints for the above problem.