# The text of underbrace overlaps with the text of document

I am using the underbrace to explain some equations, but the text of the underbrace always overlaps the text of my document. Is there any way to solve this issue?

\documentclass{article}
\usepackage{amsmath}

\begin{document}
$$\mathbf{\Xi}_{p}=\left\lbrace\smash{\underbrace{0,0,\ldots,0}_\text{p+1 copies}},\mathbf{\Xi}_{int},\smash{\underbrace{1,1,\ldots,1}_\text{p+1 copies}} \right\rbrace,$$
onto $\bar{n}$ degrees of freedom, $p-1$th order function space $\bar{\mathcal{N}}_{\bar{n},p-1}=span\left\lbrace{N}_{i,p-1}\right\rbrace$ defined by knot vector:
\end{document}

• Off-topic: As "span" appears to be a math operator, it should probably be typeset with upright letters instead of math italic letters. Since you're using the amsmath package, I recommend you set up \DeclareMathOperator{\span}{span} in the preamble and write ...\span\lbrace{N}_{i,p-1}\rbrace... in the body of the document. – Mico Aug 23 '16 at 4:52

\documentclass{article}
$$\mathbf{\Xi}_{p}=\lbrace\underbrace{0,0,\ldots,0}_\text{p+1 copies},\mathbf{\Xi}_{int},\underbrace{1,1,\ldots,1}_\text{p+1 copies} \rbrace,$$
onto $\bar{n}$ degrees of freedom, $p-1$th order function space $\bar{\mathcal{N}}_{\bar{n},p-1}=span\left\lbrace{N}_{i,p-1}\right\rbrace$ defined by knot vector: