Is not closed beneath subtraction (that is, subtracting one particular natural from Yet another does not usually end in An additional natural), implies that N displaystyle mathbb N is actually a commutative monoid with identity element 0. It's really a no cost monoid on just one generator. This commutative https://www.4shared.com/office/QQ8Xx6fbge/Cureayu_Wellness_Solutions_for.html