Show that G is ambiguous.

The word w = $\bf a$ $\bf\mid$ $\bf b$ $\bf a$ has the following two left most derivations

R	$$\Rightarrow$$	RR
	$$\Rightarrow$$	R $$\bf\mid$$ RR
	$$\Rightarrow$$	$$\bf a$$ $$\bf\mid$$ RR
	$$\Rightarrow$$	$$\bf a$$ $$\bf\mid$$ $$\bf b$$R
	$$\Rightarrow$$	$$\bf a$$ $$\bf\mid$$ $$\bf b$$$$\bf a$$

R	$$\Rightarrow$$	R $$\bf\mid$$ R
	$$\Rightarrow$$	$$\bf a$$ $$\bf\mid$$ R
	$$\Rightarrow$$	$$\bf a$$ $$\bf\mid$$ RR
	$$\Rightarrow$$	$$\bf a$$ $$\bf\mid$$ $$\bf b$$R
	$$\Rightarrow$$	$$\bf a$$ $$\bf\mid$$ $$\bf b$$$$\bf a$$

This shows that G is ambiguous.