\[\begin{array}{rrcl}
(1) & B &\longrightarrow& F \\
(2) & B &\longrightarrow& F \orop B \\
(3) & F &\longrightarrow& L \\
(4) & F &\longrightarrow& L \andop F\\
(5) & L &\longrightarrow& \tt \\
(6) & L &\longrightarrow& \ff\\
(7) & L &\longrightarrow& (B)
\end{array}\]