An property of a set whereby an operation on members of the set always produces a member of the same set
For example, Integers are closed under addition and multiplication like 1+1=2, where 2 is an integer (By closure of integers under multiplication and addition)
Commutativity (交换律)
The order in which the operands are taken does not affect the result of the operation
Addition & multiplication are commutative
x+y = y+x
Associativity (结合律)
Do not need to worry about the placement of parentheses in expressions with more than two operands
Addition & multiplication are associative
Distributivity (分配律)
Multiplication distributes over addition
x * (y + z) = (x * y) + (x * z)
Trichotomy (三分法)
For any two given inputs, there are exactly three possible outcomes. One of the outcomes must be true
