Subtraction follows several important patterns. It is anti-commutative, which means that changing the order will change the sign of the answer. It is not associative law, that is, when a subtraction exceeds two numbers, the order of subtraction is very important. Subtracting 0 does not change a number.

Subtraction also follows predictable rules related to addition and multiplication. These laws can be proved, starting with the subtraction of integers and summarizing them with real numbers and other things. Continue the general binary operation of these patterns and learn in abstract algebra.

Primary school mathematics:

Primary school mathematics is to teach children a series of knowledge about number, four operations, the calculation formula of figure and length, unit conversion and so on through textbooks, which lays a good mathematical foundation for junior high school and daily life calculation. Frieden Noel, a Dutch educator, said: "Mathematics comes from reality and must be rooted in reality and applied to reality."