You are the newest member of the Public Defender's office. Please draft a legal memorandum as to whether Dan has any justifiable defences based on the following facts:

Al went to Dan's gun shop to purchase a handgun and ammunition. Dan showed Al several pistols. Al selected the one he wanted and handed Dan five $100 bills to pay for it. Dan put the unloaded pistol and a box of ammunition in a bag and placed it on the counter. While Al was filling out the necessary registration papers, Dan went to the cash register to make change. As he was doing so, Dan noticed that the bills Al had handed him were counterfeit, and he exclaimed, "You rotten bum! You've given me phony money."

At that moment, Al grabbed the bag that had the gun and ammunition in it and fled from the gun shop. Dan grabbed a loaded pistol he kept under the counter and ran after Al, yelling at him to stop. As Dan pursued Al down the street, he fired a shot into the air, and yelled, "If you don't stop, the next shot will stop you." Al kept running, and, as he did so, he loaded a cartridge into the pistol he had fled the gun shop with, turned, and shot toward Dan. The bullet struck Dan.

Only address defences that are applicable based on the facts.