➋ Subtraction is the inverse operation of addition.
p + q = r
r - q = p
r - p = q
If p or q is greater than r, the result is not a natural number.
By defining integers to contain 0 and negative numbers, they become closed under subtraction.
---------------------------------
Natural numbers are closed under addition.
Subtraction is the inverse operation of addition.
p + q = r
r - q = p
r minus p equals q
If p or q is greater than r, the result is not a natural number.
By defining integers to contain 0 and negative numbers, they become closed under subtraction.
