Chapter 13.1, Problem 28E

a) Explain what the productions are in a grammar if the Backus−Naur form for productions is as follows:

   $\begin{array}{l}\langle \exp ression\rangle ::=\left(\langle \exp ression\rangle \right)|\\ \langle \exp ression\rangle +\langle \exp ression\rangle |\\ \langle \exp ression\rangle +\langle \exp ression\rangle |\\ \langle \mathrm{var}iable\rangle \\ \langle \mathrm{var}iable\rangle ::=x|y\end{array}$

b) Find a derivation tree for $\left(x*y\right)+x$ in this grammar.