\subsection{length}
\label{lablength}
\noindent Name: \textbf{length}\\
\phantom{aaa}computes the length of a list or string.\\[0.2cm]
\noindent Library name:\\
\verb|   sollya_obj_t sollya_lib_length(sollya_obj_t)|\\[0.2cm]
\noindent Usage: 
\begin{center}
\textbf{length}(\emph{L}) : \textsf{list} $\rightarrow$ \textsf{integer}\\
\textbf{length}(\emph{s}) : \textsf{string} $\rightarrow$ \textsf{integer}\\
\end{center}
Parameters: 
\begin{itemize}
\item \emph{L} is a list.
\item \emph{s} is a string.
\end{itemize}
\noindent Description: \begin{itemize}

\item \textbf{length} returns the length of a list or a string, e.g. the number of elements
   or letters.

\item The empty list or string have length 0.
   If \emph{L} is an end-elliptic list, \textbf{length} returns +Inf.
\end{itemize}
\noindent Example 1: 
\begin{center}\begin{minipage}{15cm}\begin{Verbatim}[frame=single]
> length("Hello World!");
12
\end{Verbatim}
\end{minipage}\end{center}
\noindent Example 2: 
\begin{center}\begin{minipage}{15cm}\begin{Verbatim}[frame=single]
> length([|1,...,5|]);
5
\end{Verbatim}
\end{minipage}\end{center}
\noindent Example 3: 
\begin{center}\begin{minipage}{15cm}\begin{Verbatim}[frame=single]
> length([| |]);
0
\end{Verbatim}
\end{minipage}\end{center}
\noindent Example 4: 
\begin{center}\begin{minipage}{15cm}\begin{Verbatim}[frame=single]
> length([|1,2...|]);
infty
\end{Verbatim}
\end{minipage}\end{center}
