Natural numbers (\mathbb{N}): The counting numbers {1, 2, 3, .. } are commonly called natural numbers; however, other definitions include 0, so that the non-negative integers {0, 1, 2, 3, .. } are also called natural numbers [REF].
Rational numbers (\mathbb{Q}): Numbers that can be expressed as a ratio of an integer to a non-zero integer [REF].