@property<EOL><INDENT>def Hill(self):<DEDENT>
if self.__Hill:<EOL><INDENT>return self.__Hill<EOL><DEDENT>else:<EOL><INDENT>self.__Hill = atoms_to_Hill(self.atoms)<EOL>return self.__Hill<EOL><DEDENT>
r'''Hill formula of a compound. For a description of the Hill system,
        see :obj:`thermo.elements.atoms_to_Hill`.

        Examples
        --------
        >>> Chemical('furfuryl alcohol').Hill
        'C5H6O2'