Properties of CFLs Intuitively, more should be decidable or recognizable, since CFLs are more restricted than recognizable languages. Also useful for other properties. But lecture won't cover these, see HU book. Uses CFL closure properties already seen. Uses the previous undecidability of one CFL property.
G is unambiguous.
Assume Ga is ambiguous. Then there must exist two similar leftmost derivations in G for xa. But, this is impossible, since G is unambiguous. So Ga must be unambiguous.