 In this understanding, the respective sets without zero are called strictly positive real numbers and strictly negative real numbers, and are noted ℝ+* and ℝ−*.The notation R"n" refers to the Cartesian product of "n" copies of R, which is an "n"-dimensional vector space over the field of the real numbers; this vector space may be identified to the "n"-dimensional space of Euclidean geometry as soon as a coordinate system has been chosen in the latter.For example, a value from R3 consists of three real numbers and specifies the coordinates of a point in 3‑dimensional space.