This document discusses properties and operations of integer numbers. It defines integers as ordered pairs of natural numbers, and defines addition, subtraction, multiplication and division of integers. It proves several theorems about these operations, such as the addition of integers being well-defined regardless of the pairs used, and properties like commutativity and the existence of an identity element. It also classifies integers as positive, negative or zero based on the ordered pairs, and proves theorems about the results of operations between integers of different classes.