Puzzle #244: Buckets

You have two buckets. One will hold five liters of water, and the other will hold three liters. They have no markings. If you fill a bucket from the faucet, you must fill it full. If you pour from one bucket into the other, you can stop only when the first bucket is empty or the second bucket is full. You can also discard all of the water in a bucket.

How can you end up with four liters of water in the five-liter bucket?

Submit your answer to Gene Wirchenko <genew@telus.net>. Your answer should be in the form of a proof. That means to show how your answer must be correct. The deadline is Wednesday, February 7, 2018 at noon Pacific Time. I will post the answer shortly after.