Counting Method / June 6, 2018 / Willow Rider
Like the natural numbers, Z is closed under the operations of addition and multiplication, that is, the sum and product of any two integers is an integer. However, with the inclusion of the negative natural numbers, and, importantly, 0, Z (unlike the natural numbers) is also closed under subtraction. The integers form a unital ring which is the most basic one, in the following sense: for any unital ring, there is a unique ring homomorphism from the integers into this ring. This universal property, namely to be an initial object in the category of rings, characterizes the ring Z.
Integers are used in everyday life. A debt or a loss is often expressed with a negative integer. A gain is usually expressed with a positive integer. When the temperature is warmer than the zero point of the temperature scale, it is represented with a positive sign; when it is colder than the zero point, it is represented with a negative sign.