%%
%% The LaTeX Companion, 3ed
%%
%% Example 9-4-6 on page I-682 in "Defining new alphabet identifiers".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{135.0pt}
%!TEX program = lualatex
  
%StartShownPreambleCommands
\usepackage{unicode-math}
\setmathfontface\mathttit{texgyrecursor-italic.otf}
%StopShownPreambleCommands

\begin{document}
$\mathttit{ttit} \approx \mathtt{tt} + \mathit{italic}$
\end{document}