\Header{Constants}{Built-in Constants}
\alias{LETTERS}{Constants}
\alias{letters}{Constants}
\alias{month.abb}{Constants}
\alias{month.name}{Constants}
\alias{pi}{Constants}
\keyword{sysdata}{Constants}
\begin{Usage}
\begin{verbatim}
LETTERS
letters
month.abb
month.name
pi
\end{verbatim}
\end{Usage}
\begin{Value}
\R\ has a limited number of built-in constants (there is also a rather
larger library of data sets which can be loaded with the function
\texttt{data}).

The following constants are available:
\begin{ldescription}
\item[\texttt{LETTERS}] the 26 upper-case letters of the Roman alphabet;
\item[\texttt{letters}] the 26 lower-case letters of the Roman alphabet;
\item[\texttt{month.abb}] the three-letter abbreviations for the English
month-names;
\item[\texttt{month.name}] The English names for the months of the year;
\item[\texttt{pi}] the ratio of the circumference of a circle to its diameter.
\end{ldescription}
\end{Value}
\begin{SeeAlso}
\texttt{\Link{data}}.\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
  all(nchar(letters) == 1)                    # TRUE
  all(month.abb == substr(month.name, 1, 3))  # TRUE
\end{ExampleCode}
\end{Examples}

