如何在使用LaTeX的数学模式下指示一个短划线？

There are four kinds of 'dashes' in LaTeX: hyphen, en-dash(--), em-dash(---) and minus $-$. They are used for, respectively, hyphenation and joining words, indicating a range, punctuation, and a mathematical symbol. My question is: how do I indicate an en-dash (range) in math mode? (as in There are four kinds of 'dashes' in LaTeX: hyph