# Cannot use \tex inside of \title{…}

I cannot use \tex inside the \title{...} since it fails on the \maketitle command. When I remove the \tex, the file is built correctly.

\begin{titlepage}
\title{
\normalfont
\LARGE University name \\[25pt]
\rule{\linewidth}{1pt} \\[0.4cm]
\huge Semestral work XXX \\
\rule{\linewidth}{1pt} \\[0.6cm]
\Large Rewritten in the \tex typesetting system \\[0.5cm]  % probable cause %
}
\author{Nikolas Charalambidis}
\date{\normalsize{7. 5. 2019}}
\maketitle                                                      % failing %
\thispagestyle{empty}
\end{titlepage}


The error is (I use TexMaker):

Undefined control sequence.@title ...\[0.6cm] \Large Rewritten in the \textypesetting system \[0.5cm] \maketitle

• One very very important thing, you have two possibilities: either using \title{stuff} and \maketitle to get the predefined title page; or use titlepage to define a title page of your own. Do not mix them up. – Johannes_B May 9 at 6:52

(La)TeX control sequences are case-sensitive, for example \Sigma is different from \sigma. The command \tex is not defined yet. You need \TeX.
In your document, \TeX is followed by a space. The compiler ignores this. To add the space, you may want to read this question. Personally I prefer the \TeX\ typesetting to the \TeX{} typesetting.
Note that TeX is not LaTeX. You may want to write \LaTeX there, because your document is written in LaTeX, not TeX. \LaTeXe, to produce "LaTeX 2e", fits even better.