This one is a little harder to explain than my earlier post. Your attention should be focused on the line in the middle that begins “N(T) = …” and ends with a diamond. That line contains three copies of the letter R: the first is in italics, while the latter two are in a sans serif font. What is astonishing is that the first and third copies of the letter R mean the same thing (they both denote the set of real numbers), while the middle one (in the same font as the third) denotes a completely separate thing, the image of a linear transformation. (In case you are wondering, these notations are consistent throughout the book (*Linear Algebra* by Friedberg, Insel, and Spence), it’s not like there’s just a typo here.) There are at least four *major* problems with this notation; yet somehow, this book is in its 5th edition and still using it.

(In other respects it’s a very good book! But the conscious notational choices of the authors are just amazingly awful.)