Get together with another person, and do the following exercise. Get four playing cards with different values. Shuffle them, and put them face-down on the table. One of you has to sort the cards, from low to high. This person is allowed to move the cards around, but is not allowed to look at their face sides. However, this person is allowed to point at two of the cards, after which the other one picks up those two cards, looks at their faces, and then puts them back and says which of the two is higher. Count how often such a comparison is made. Once the first person is satisfied that the cards are sorted, they are turned over to check if they are indeed sorted correctly.

In this exercise, the first person basically takes the role of a computer program, that follows instructions without actually understanding values. The second person takes the role of the computer processor, which can perform certain functions for the program, in this case, comparing numbers.

If you did not manage to sort the cards correctly, think about how you can accomplish this task under the given circumstances, and after that try it once more. If you did sort them correctly and needed more than six comparisons, think about how you can do it with six comparisons. If you managed to do it with six comparisons, think about if you can do it with less than six. If you did it with less than six, think about if your procedure is guaranteed to sort any collection of four cards.