2. It is the number that counts none or nothing.
3. It is marked 0 in our usual numeral writing.
4. The ancient Romans, however, had no numeral for it. Apparently, they did not think of zero as a number.
5. 0 is what you get when you take away 17 from 17, or when you subtract any number from itself.
6. If you add 0 to 23, you get 23; and if you add 0 to any number, you get that number unchanged.
7. If you subtract 0 from 48, you get 48; and if you subtract 0 from any number, you get that number unchanged.
8. If you multiply 0 by 71, you get 0; and if you multiply together 0 and any number, you get 0.
9. Usually you are not allowed to divide by 0: that is against the rules of arithmetic.
10. But if you do, and if you divide 12 by 0, for example—and there are times when this is not wrong—the result is called infinity and is marked ∞, a sign that is like an 8 on its side.
This is not all the story of zero; it is one of the most important of numbers. But, if you know these statements about zero, and have had some practice in applying them, you have a good understanding of zero. Incidentally, a mechanical brain knows all these statements about zero and a few more; they must be built into it.