

   BBuuiilltt--iinn CCoonnssttaannttss

        LETTERS
        letters
        month.abb
        month.name
        pi

   VVaalluuee::

        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 `data').

        The following constants are available:

    LETTERS: the 26 upper-case letters of the Roman alphabet;

    letters: the 26 lower-case letters of the Roman alphabet;

   month.abb: the three-letter abbreviations for the English
             month-names;

   month.name: The English names for the months of the year;

         pi: the ratio of the circumference of a circle to its
             diameter.

   SSeeee AAllssoo::

        `data'.

   EExxaammpplleess::

          all(nchar(letters) == 1)                    # TRUE
          all(month.abb == substr(month.name, 1, 3))  # TRUE

