| − | Natural numbers are the nonnegative integers {0, 1, 2, 3,...}, according to most modern mathematics and logic textbooks. Older books sometimes exclude zero, as there is a long history of people thinking that zero is unnatural or not really a number. | + | '''Natural numbers''' are the nonnegative [[integer]]s {0, 1, 2, 3,...}, according to most modern [[mathematics]] and [[logic]] textbooks. Older books sometimes exclude [[zero]], as there is a long history of people thinking that zero is unnatural or not really a number. |