UGC NET CSE | October 2020 | Part 2 | Question: 62

Question

Which of the following statements are true?

1. A sentence $\alpha$ entails another sentence $\beta$ if $\beta$ is true in few worlds where $\alpha$ is true
2. Forward chaining and backward chaining are very natural reasoning algorithms for knowledge bases in Horn form
3. Sound inference algorithms derive all sentences that are entailed
4. Propositional logic does not scale to environments of unbounded size

Choose the correct answer from the options given below:

• A. $(i)$ and $(ii)$ only
• B. $(ii)$ and $(iii)$ only
• C. $(iii)$ and $(iv)$ only
• D. $(ii)$ and $(iv)$ only

Answer 1

1. A sentence α entails another sentence β  if β is true in few worlds where α is true   False  β must be true in all worlds where α is true
2. Forward chaining and backward chaining are very natural reasoning algorithms for knowledge bases in Horn form  True These algorithms are very natural and run in linear time   https://www.iiia.csic.es/~puyol/IAGA/Teoria/07-AgentsLogicsII.pdf
3. Sound inference algorithms derive all sentences that are entailed False (it is complete not  sound) The inference algorithm is sound if it derives only sentences that are entailed by Knowledge Base
4. Propositional logic does not scale to environments of unbounded size  True • Propositional logic is reasonably effective for certain tasks within an agent, but does not scale to environments of unbounded size because it lacks the expressive power to deal concisely with time, space, and universal patterns of relationships among objects. (refer Russel norvig AI book agents chapter)                                                                                     Hence ans is option D)(b) and (d) only