Read Sipser §5.1 and §5.3. Then review this overview of undecidable proof strategies.
- Outline the common strategy for proving that a language is undecidable.
- How are computation histories used in the proofs of Theorems 5.10 and 5.13?
- If $$A ≤_m B,$$ and B is a regular language, does that imply that A is a regular language? Why or why not?