In the context of combinatorial game theory, a nimber (or Grundy value) refers to a value associated with a position in a game, representing the winning strategy for that position. Nimbers are typically represented as non-negative integers or their equivalents in other forms.
A rational nimber is a nimber that can be expressed as a rational number. In the standard representation used in the context of nimbers, these values can be whole numbers or their combinations but typically do not include non-integer rational numbers like 2.15.
Since 2.15 is not an integer, it is not considered a nimber in the traditional sense of combinatorial game theory. Nimbers are generally restricted to non-negative integers, so 2.15 would not be classified as a rational nimber according to these conventions.