# Inserting mathematical operator in Lyx

I would like to insert the less than or equal mathematical operator in the text of a Lyx document.

Insert/Special Character/Symbols shows the symbol in the text, but compiling results in an error ("Missing character: There is no <= font Dolly-Roman/OT:mapping=tex-text;mappin").

Inserting an ERT box with \$\leqq\$ gives an "Undefined control sequence" error.

How do I insert the <= (\leqq) symbol in my text if the font that I am using does not have it?

`\leqq` is defined in the package `amssymb`, so you'll have to add a `usepackage{amssymb}` to your document.
For missing characters, there's no other solution than switching to a (math) font that has the character(s) you want. Sometimes you can do that just for a few characters. This is not recommended in most cases, as the glyphs won't have the same "feel" ("character") to them. Note that you'll have the same situation when just inserting `\$\leqq\$` in your document to get the glyph: it will be taken from the active math font (probably something close to Computer Modern).