There was a farmer making his way to the market with a fox, a chicken, and some grain. He came to a clearing with a stream. There was a rickety bridge nearby, but he could only take one of his items with him across the bridge at a time. He knew if he took the grain, and left the fox with the chicken, the fox would eat the chicken. If he took the fox, the chicken would eat the grain. How do you get all of them across?