Create a lambda mirror

Question

Could you help me please, I need a mirror lambda as the sub-indice in the picture. I tried `d_{{\reflectbox{$\lambda$}}_j}´ without success.

Answer 1

Go to the webpage https://detexify.kirelabs.org/classify.html and draw the symbol. The classifier will tell you that it is the symbol \rightthreetimes from the amssymb packages.

\documentclass{article}
\usepackage{amsmath}% \begin{cases} ... \end{cases}
\usepackage{amssymb}% \rightthreetimes
\begin{document}
\[
  \begin{cases}
    d_\rightthreetimes\geq a, d_\rightthreetimes\geq b, d_\rightthreetimes\geq c\\
    a + b + c \geq 2d_\rightthreetimes\\
    a + b + c \leq 2
  \end{cases}
\]
\end{document}

Answer 2

You can use \mathpalette (you find several examples on the site).

\documentclass{article}
\usepackage{graphicx}
\makeatletter
\DeclareRobustCommand{\mlambda}{% mirror lambda
  {\mathpalette\mlambda@\relax}%
}
\newcommand{\mlambda@}[2]{%
  \reflectbox{$\m@th#1\lambda$}%
}
\makeatother
\begin{document}
$\mlambda+x_{\mlambda}$
$\lambda+x_{\lambda}$
\end{document}