%% 
%%  Example 06-05-2 
%%  Copyright (C) 2016 Herbert Voss
%% 
%% ==== 
% Show page(s) 1
%% 
%% 
\documentclass[]{screxa}
\pagestyle{empty}
\setlength\textwidth{158.31393pt}
\setlength\parindent{0pt}
\usepackage[T1]{fontenc}
%StartShownPreambleCommands
\newcommand\Let{\mathrel{%
  \mathop:\!\!=}}%  Upper case L!
\newcommand\teL{\mathrel{=\!\!\mathop:}}
%StopShownPreambleCommands
\begin{document}
$x\Let y$ $y\teL x$
\end{document}
