shorthand for domains in math

Domain shorthand can be tricky. This is a quick breakdown:

D = Domain (defined, like {1, 2, 3}) N = Natural numbers (all positive integers, starting at 1 to inf) Q = Rational numbers (written as a ratio) R = All real numbers, including all real numbers (i.e., [-inf, inf]) Z = Integers (all negative and positive [-inf, ..., 0, ..., inf])