the symbol of set of all real numbers
You can write the symbol of a number set (with double lines) using the mathbb font which is supported by amsfonts or amssymb package. $\mathbb{N}$ is the set of natural numbers, $\mathbb{Z}$ is the set of integers, $\mathbb{Q}$ is the set of rational numbers and $\mathbb{R}$ is the set of real numbers. All contents copyrighted 2000-2013 Anthony Liekens unless otherwise noted. Built with PmWiki, styled with Bootstrap.