Comp335 Introduction to Theoretical Computer Science Winter 2023 Assignment 3
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Comp335 Introduction to Theoretical Computer Science
Winter 2023
Assignment 3. Due date: March 22, by 23:59 P.M.
1. Give context-free grammars for each of the following languages.
(a) {ah bk am bn : h + k = m + n}
(b) {ai bj ak : (i = j and k 2 0) or (i 2 0 and j > k)}
2. Prove that if G is the context-free grammar defined by the productions S → aSbS ∣ bSaS ∣e then L(G) = {w e {a, b}* : na (w) = nb (w)}.
3. In each case below, show that the grammar is ambiguous, and find an equivalent unambiguous grammar.
(a) S → SS ∣ ab ∣ a
(b) S → ABA, A → aA ∣ e, B → bB ∣e
4. Design a PDA to accept each of the following languages. You may design your PDA to accept either by final state or empty stack, whichever is more convenient.
(a) {ah bk am bn : h + k = m + n}
(b) {an b : n 2 0} u {abn : n 2 0} u {an bn : n 2 0}
5. Give an example of a PDA P = (Q, Σ , Γ, δ, q0 , Z0 , F ) is a PDA, and strings x, y e Σ, α, β, γ e
(Σ u Γ)* such that (q, x, αγ)上(*) (p, y, βγ) but (q, x, α)上(*) (p, y, β) does not hold.
6. Using the methods in the text,
(a) convert the grammar G = ({S, A}, {0, 1}, {S → 0S1∣A, A → 1A0∣S∣e}, S}) to a PDA that
accepts exactly L(G).
(b) convert the PDA P = ({q0 , q1 }, {a, b}, {A, Z0 }, δ, q0 , Z0 , {q1 }), where
δ(q0 , a, Z0 ) = {(q0 , AZ0 )}, δ(q0 , b, A) = {(q0 , AA)}, δ(q0 , a, A) = {(q1 , e)} to a CFG G, such that L(G) = L(P).
7. Convert the following grammars into Chomsky Normal Form
(a) S → ASB ∣ e, A → aAS ∣ a, B → SbS ∣ A ∣bb.
(b) S → 0A0 ∣ 1B1 ∣ BB, A → C, B → S ∣ A, C → S ∣e.
8. Use the Pumping Lemma for CFL’s to show that the following languages are not Context-Free.
(a) {w e {a, b, c}* : na (w) < nb (w) and na (w) < nc (w)}
(b) {an bj ck dl : n < k and j < l}
2023-05-02