# Problems with language?

I don't know why this code doesn't work:

\documentclass[11pt]{article}
\usepackage{fullpage}
\usepackage{amsfonts}
\usepackage[utf8]{inputenc}
\usepackage{amsthm}
\newtheorem{theorem}{Teorema}
\theoremstyle{definition}
\newtheorem{definition}{Definição}
\begin{document}

\begin{definition}

Um conjunto $H$ com uma operação binária associativa é chamado de semigrupo.

\end{definition}

\begin{definition}

Um semigrupo $H\subset \mathbb{N}$ é chamado de numérico quando $0\in H$, $L=\mathbb{N}-H$ é finito e $1\in L$. Os elementos $1=l_1\lt l_2\ldots\lt l_g$ de $L$ são chamados de lacunas de $H$ e os elementos $0=n_0\lt n_1\lt\ldots$ de $H$ são chamados de não-lacunas de $H$. A quantidade de lacunas de $H$ é chamada de gênero de $H$.

\end{definition}

\begin{definition}

Um semigrupo numérico $H$ é chamado de hiperelíptico quando $n_1=2\in H$.

\end{definition}

\end{document}


Log:

! Undefined control sequence.
l.19 ... finito e $1\in L$. Os elementos $1=l_1\lt l_2\ldots\lt l_g$ de $L$ ...
The control sequence at the end of the top line
of your error message was never \def'ed. If you have
misspelled it (e.g., \hobx'), type I' and the correct
spelling (e.g., I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.
! Undefined control sequence.
l.19 ...in L$. Os elementos$1=l_1\lt l_2\ldots\lt
l_g$de$L$são chamados...  It's something to do with the language? Thanks • There is no \lt command as far as I know. Use < instead if you mean that symbol. – user31729 Sep 19 '14 at 4:09 • At several places \lt is used inside math. What it is supposed to mean? – Heiko Oberdiek Sep 19 '14 at 4:10 • – Adam Liter Sep 19 '14 at 4:10 • @user108205: I retagged your question, since it's not connected to languages but to an error due to an unknown macro named \lt – user31729 Sep 19 '14 at 4:29 • @Aradnix Thank you very much, I didn't know it! – user108205 Sep 23 '14 at 20:31 ## 1 Answer I think, \lt should mean less than, there is no such command however, as far as I know. It's easy to define such a command with this meaning, if needed: \newcommand{\lt}{\ensuremath{<}}%  There are some commands called \le and \ge meaning <= etc. In addition, if needed, a \gt can be defined accordingly: \newcommand{\gt}{\ensuremath{>}}%  \documentclass[11pt]{article} \usepackage{fullpage} \usepackage{amsfonts} \usepackage[utf8]{inputenc} \usepackage{amsthm} \newtheorem{theorem}{Teorema} \theoremstyle{definition} \newtheorem{definition}{Definição} \newcommand{\lt}{\ensuremath{<}}% \begin{document} \begin{definition} Um conjunto$H$com uma operação binária associativa é chamado de semigrupo. \end{definition} \begin{definition} Um semigrupo$H\subset \mathbb{N}$é chamado de numérico quando$0\in H$,$L=\mathbb{N}-H$é finito e$1\in L$. Os elementos$1=l_1 \lt l_2\ldots \lt l_g$de$L$são chamados de lacunas de$H$e os elementos$0=n_0\lt n_1\lt\ldots$de$H$são chamados de não-lacunas de$H$. A quantidade de lacunas de$H$é chamada de gênero de$H$. \end{definition} \begin{definition} Um semigrupo numérico$H$é chamado de hiperelíptico quando$n_1=2\in H\$.

\end{definition}

\end{document}
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