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CS21 Decidability and Tractability Lecture 6 January 17, 2024 Context-free grammars and languages • languages recognized by a (N)FA are exactly the languages described by regular expressions, and they are called the regular languages Copyright By PowCoder代写 加微信 powcoder • languages recognized by a NPDA are exactly the languages described by context-free grammars, and they

CS21 Decidability and Tractability Lecture 23 February 28, 2024 • language L is in coNP iff its complement (co-L) is in NP • it is believed that NP ≠ coNP Copyright By PowCoder代写 加微信 powcoder • note: P = NP implies NP = coNP – proving NP ≠ coNP would prove P ≠ NP –

CS21 Decidability and Tractability Lecture 10 January 26, 2024 Turing Machine diagrams start state qreject Copyright By PowCoder代写 加微信 powcoder b → R transition label: (tape symbol read → (1 accept + 1 reject) tape symbol written, direction moved) – a → R means “read a, move right” – a → L means “read a,

CS21 Decidability and Tractability Lecture 21 February 23, 2024 • NP-complete problems: independent set, vertex cover, clique… • NP-complete problems: Hamilton path and cycle,Traveling Salesperson Problem Copyright By PowCoder代写 加微信 powcoder • NP-complete problems: Subset Sum • NP-complete problems: NAE-3-SAT, max cut February 23, 2024 CS21 Lecture 21 2 “x1” “x2 ” February 23, 2024

CS21 Decidability and Tractability Lecture 3 January 8, 2024 NFA diagrams (single) start state • At each step, several choices for next state – if possible to reach accept, then input accepted Copyright By PowCoder代写 加微信 powcoder January 8, 2024 CS21 Lecture 3 2 transitions: (several) accept states • may have several with a given

CS21 Decidability and Tractability • undecidable problems – computation histories – surprising contrasts between Copyright By PowCoder代写 加微信 powcoder decidable/undecidable • Rice’s Theorem • Post Correspondence Problem (skip) • Beyond RE and co-RE • Recursion Theorem February 5, 2024 CS21 Lecture 14 2 Dec. and undec. problems • two problems regarding Context-Free Grammars: – does

CS21 Decidability and Tractability Lecture 4 January 10, 2024 Regular expressions • R is a regular expression if R is – a, for some a ∈ Σ Copyright By PowCoder代写 加微信 powcoder – ε, the empty string – Ø, the empty set – (R1 ∪ R2), where R1 and R2 are reg. exprs. –(R1 ∘R2),whereR1

CS 21 Decidability and Tractability Winter 2024 Posted: January 17 Solution Set 1 If you have not yet turned in the Problem Set, you should not consult these solutions. Copyright By PowCoder代写 加微信 powcoder 1. We need to define a language that has the same computational power as the function f; that is, given f