You have a 4-gallon and a 9-gallon container, an unmarked container, and a huge water supply.
You want to end up with exactly 6 gallons in the unmarked container.
(YES: the unmarked container > 6 gallons!)
Your mission is to do it in exactly 9 moves, and using the MINIMUM number of gallons of water
from the water supply.
A "move" is any pouring, filling or emptying.
For example, filling the 9-gal from the water supply,
then pouring it to fill the 4-gal container,
then emptying it is 3 moves: fill - pour - empty.
How do you do it?