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If a system uses strict 2PL, it can prevent from having any phantom read issue.

The following schedule is serializable. R1(A), W1(A), R2(C), W2(C), R2(B), W2(B), R1(C), R1(B), W1(B)  Note: R, W refer to Read and Write operations. A, B, C refer to the data items. 1, 2 refer to the transaction id. For example, R1(A) means Transaction 1 reads A. 

The following schedule is unrecoverable: R1(A), R1(B), R2(A), W2(B), Commit_2, W1(B), Abort_1.                          Note: R, W refer to Read and Write operations. A, B, C refer to the data items. 1, 2 refer to the transaction id. For example, R1(A) means Transaction 1 reads A.  Commit_2 means Transaction 2 commits.  Abort_1 means Transaction 1 aborts. 

Which of the following is a contradictory sentence (a sentence that can never be true)?

What have you proven when you derive both Ψ and ¬Ψ in an indirect proof?

Complete this short indirect proof. Fill in the missing line. (P → Q) Premise ¬Q Premise |_P AIP (Assumption for Indirect Proof) |_[BLANK-1]  Modus Ponens [BLANK-2], [BLANK-3] ¬P 4,2, Contradiction, IP What should line 4 be?

Cell phones should be silenced when watching a theater performance.

Photovoltaic cells convert light energy from the sun and store this energy in batteries for easy use.

When examining Pablo Picasso’s art, his paintings often portray people with distorted faces.

Birth defects are common among addicted mothers, such as chronic lung diseases.