Let's play a game. I'll be the computer, and you be the human, OK? I'll hand you a slip of paper on which will be printed two numbers -- all numbers are nonnegative integers. Then you can reduce one or both of the two numbers by any positive integer amount, but you can't make either number negative, and then you can hand me back the slip of paper. We take turns reducing one or both of the numbers until one of us reduces both numbers to 0, winning the game.

What is a good strategy for winning the game?

Would you like to play the game while you think some more about it?

Source: reference will be supplied at a later date.