III. return the bill to Congress for clarification on some point within the bill IV. allow the Congress to pocket veto the bill, thereby allowing the bill to become law without his signature a.
Decidability. Definition: A language is called decidable if there exists a method-any method at all-to determine whether a given word belongs to that language or not. Working hypothesis I: Decidability is well defined above.roof: Surely, a decidable language is recognizable. Moreover, if a language is decidable, then so is its complement, and hence that complement is recognizable. Now suppose a language L and its complement are recognizable. Let A be a recognizer for L, and B for its complement.
Theorem 4.7 (4.6) is a decidable language Proof ideas: For a CFG and a string: First idea: Go through all derivationsgenerated by checking whether any is aderivation of.Since there are inï¬nitely many derivations this idea does not work.If does not generate  the algorithm doesnât halt.roblem 3 decidability of CFL Problem: for an CFL and string doesbelong to ?, i.e. is there a CFG such that? Language: a CFL and string Theorem 4.9 Every context-free language is decid-able Decidable Problems Concerning Context-Free Languages â p.14/33.