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P6. Let Z={a,b,c}. Show that (a) * is countable (b) The set of all languages over is uncountable P7. It is known that {: G is CFG and L(G) = {*} is undecidable. Show that language { : G1, G2 are CFG and L(G1) = L(G2)} is also undecidable. P8. Show that the language {:M is T.M. and L(M) is nonempty} is recognizable