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|context> => |context: context free grammar>

supported-ops |*> => |op: r1> + |op: r2> + |op: r3> + |op: r4> + |op: r5> + |op: r6> + |op: r7> + |op: r8> + |op: random-rule>
r1 |*> #=> rewrite(|_self>, |S>, |x>)
r2 |*> #=> rewrite(|_self>, |S>, |y>)
r3 |*> #=> rewrite(|_self>, |S>, |z>)
r4 |*> #=> rewrite(|_self>, |S>, |S + S>)
r5 |*> #=> rewrite(|_self>, |S>, |S - S>)
r6 |*> #=> rewrite(|_self>, |S>, |S * S>)
r7 |*> #=> rewrite(|_self>, |S>, |S / S>)
r8 |*> #=> rewrite(|_self>, |S>, |(S)>)
random-rule |*> #=> apply(pick-elt the-list-of |rules>, |_self>)

supported-ops |rules> => |op: the-list-of>
the-list-of |rules> => |op: r1> + |op: r2> + |op: r3> + |op: r4> + |op: r5> + |op: r6> + |op: r7> + |op: r8>
----------------------------------------