[Tex/LaTex] Identifying a single math symbol

Question

I would like to reproduce the following symbol:

• The proof wiki does not seem to refer to that symbol,
• I did not find any font corresponding in the Math alphabets and the mathalfa package by Michael Sharpe
• My pdf reader tells me that the embedded fonts are

But that is related to the OCR technique and does probably not reflect the font actually used.

• What the font was not really conclusive:

• Detextify and Write Math were of no help.

• I did not manage to find it in the LaTeX font catalogue nor in the The Comprehensive LATEX Symbol List

Does someone have an idea? Do I miss something?

EDIT: in context,

EDIT 2: when I copy / paste that symbol from my pdf viewer, it yields a 2, could that be a 2? It really looks like an L!

That also is probably related to some error of the OCR.

Answer 1

The glyph in question appears to be very similar to the uppercase L provided in the "curly" math font of the MathTime Professional 2 complete font set (commercial fonts).

It can be used in three ways:

Method 1: change all math fonts to MTPro2

\documentclass{article}
\usepackage[mtpccal]{mtpro2}

\begin{document}
A set of strings is in the class $\mathcal{L}_{*}$ if and only if 
$A$ is \dots within time $P(n)$, for some polynomial $P(n)$.
\end{document}

The package option mtpccal assigns the "curly" script variant to \mathcal. Depending on the font selections in your document, the other MTPro2 fonts may or may not be good matches with the body text (for example, it is a bad match with Computer Modern, as shown here). This also prevents use of the "standard" calligraphic fonts, if needed.

Method 2: declare an additional symbol font (preserves existing settings for all other math)

\documentclass{article}
\DeclareSymbolFont{curly}{U}{mt2ms}{m}{n}
\DeclareSymbolFontAlphabet{\mathcurly}{curly}

\begin{document}
A set of strings is in the class $\mathcurly{L}_{*}$ if and only if 
$A$ is \dots within time $P(n)$, for some polynomial $P(n)$.
\end{document}

This is more flexible than Method 1. You can make your own choices about math fonts and use the curly font only as needed. The disadvantage is that another full alphabet is used, which may or may not be an issue depending on the complexity of your document.

Method 3: import this single symbol from MTPro2 only

Using the methodology from Importing a Single Symbol From a Different Font and borrowing the relevant code from mtpro2.sty and umt2ms.fd, this method brings in only the "L" from the MathTime Curly math font. It gives the same output as Method 2, but an additional alphabet is not used.

\documentclass{article}
\DeclareFontFamily{U}{mt2ms}{\skewchar\font42}
\DeclareFontShape{U}{mt2ms}{m}{n}{<-7>mt2mcf<7-9>mt2mcs<9->mt2mct}{}
\DeclareSymbolFont{MTPcurly}{U}{mt2ms}{m}{n}
\DeclareMathSymbol{\cobhamclass}{0}{MTPcurly}{'114}

\begin{document}
A set of strings is in the class $\cobhamclass_{*}$ if and only if 
$A$ is \dots within time $P(n)$, for some polynomial $P(n)$.
\end{document}