notation of a real coordinate system of n dimension

Question

I observe that books write a bold faced R,

But the professors write R preceded by a bar. Is that I, denoting infinitism? I am not sure if it is I, its more of a vertical bar. Is it universal, or incidentally I am coming across only such professors?

|R?

Answer 1

A standard convention for writing bold face in mediums that aren't amenable to heavy/thick strokes is to instead double some of the lines in a character; e.g. with the diagonal line in $\mathbb{Z}$.

This is called "blackboard bold".

(although since so much math is done on blackboards, $\mathbb{R}$ has partially taken over from $\mathbf{R}$ as the standard notation for the reals)

Answer 2

That bar is used so that alphabet R becomes free for further usage.$\mathbb{R}$ denotes set of real number and R is simple alphabet which can be used for any purpose. But if we denote R as set of real number then alphabet R gets freezed for further usage