\subsection{atanh}
\label{labatanh}
\noindent Name: \textbf{atanh}\\
\phantom{aaa}the hyperbolic arctangent function.\\[0.2cm]
\noindent Library names:\\
\verb|   sollya_obj_t sollya_lib_atanh(sollya_obj_t)|\\
\verb|   sollya_obj_t sollya_lib_build_function_atanh(sollya_obj_t)|\\
\verb|   #define SOLLYA_ATANH(x) sollya_lib_build_function_atanh(x)|\\[0.2cm]
\noindent Description: \begin{itemize}

\item \textbf{atanh} is the inverse of the function \textbf{tanh}: \textbf{atanh}($y$) is the unique number 
   $x \in [-\infty; +\infty]$ such that \textbf{tanh}($x$)=$y$.

\item It is defined only for $y \in [-1; 1]$.
\end{itemize}
See also: \textbf{tanh} (\ref{labtanh})
