Arithmetic Course/Number Operation/Subtraction

Subtraction
Subtraction is an operation where one number is deducted from another. It can be represented by
 * A - B

Operation

 * a - b = -b + a
 * a - b - c = a - (b + c) = (a - b) - c

Rules
Any number subtract zero is equal to the number
 * a - 0 = a

Any number subtract to itself equals zero
 * a - a = 0

Any number subtract its negative is doubled
 * a - (-a) = 2a