Integers
The negative of a positive integer is defined as a number that produces 0 when it is added to the corresponding positive integer. Negative numbers are usually written with a negative sign (a minus sign). As an example, the negative of 7 is written −7, and 7 + (−7) = 0. When the set of negative numbers is combined with the set of natural numbers (which includes 0), the result is defined as the set of integer numbers, also called integers, Z also written . Here the letter Z comes from German Zahl, meaning "number". The set of integers forms a ring with operations addition and multiplication.