[Tex/LaTex] Symbols for left and right limits

amsmathluatexmath-modesymbols

I am using lualatex, are there symbols for left and right limits, like small "-" and "+" to put above the numbers? For now I use 

\documentclass[a4paper,12pt]{book}
\usepackage{fontspec}
\usepackage{polyglossia}
\usepackage{amsmath,empheq}
\usepackage{mathtools}
\usepackage{amscd}
\usepackage{amsxtra}
\usepackage{unicode-math}                 

\begin{document}
\[
\lim_{x \rightarrow 1^{+}} f(x)
\] 
\[
\lim_{x \rightarrow 1^{-}} f(x)
\]
\end{document}

which I feel is not right because the default "+" and "-" are operators and their size and spacing might not be the best for this use.

Best Answer

Infix operators like + and - lose their infix status (and the extra space that implies) if used on their own in this way. Also as noted by egreg, in a superscript the operators would get no space even used as an infix operator.

What you have is the standard markup.

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