\subsection{acos}
\label{labacos}
\noindent Name: \textbf{acos}\\
\phantom{aaa}the arccosine function.\\[0.2cm]
\noindent Library names:\\
\verb|   sollya_obj_t sollya_lib_acos(sollya_obj_t)|\\
\verb|   sollya_obj_t sollya_lib_build_function_acos(sollya_obj_t)|\\
\verb|   #define SOLLYA_ACOS(x) sollya_lib_build_function_acos(x)|\\[0.2cm]
\noindent Description: \begin{itemize}

\item \textbf{acos} is the inverse of the function \textbf{cos}: \textbf{acos}($y$) is the unique number 
   $x \in [0; \pi]$ such that \textbf{cos}($x$)=$y$.

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