<?xml version="1.0"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1 plus MathML 2.0//EN" "http://www.w3.org/TR/MathML2/dtd/xhtml-math11-f.dtd" [ <!ENTITY mathml "http://www.w3.org/1998/Math/MathML"> ]> <math display="block" xmlns="&mathml;"> <mi>f ̲</mi> <mi>-</mi> <mo>+</mo> <mo> -</mo> <mo>̲</mo> </math>