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chapter7

# chapter7 - Logic Agents and Propositional Logic CHAPTER 7...

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C H A P T E R 7 H A S S A N K H O S R A V I S P R I N G 2 0 1 1 Logic Agents and Propositional Logic

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Knowledge-Based Agents KB = knowledge base A set of sentences or facts e.g., a set of statements in a logic language Inference Deriving new sentences from old e.g., using a set of logical statements to infer new ones A simple model for reasoning Agent is told or perceives new evidence E.g., A is true Agent then infers new facts to add to the KB E.g., KB = { A -> (B OR C) }, then given A and not C we can infer that B is true B is now added to the KB even though it was not explicitly asserted, i.e., the agent inferred B
Wumpus World Environment Cave of 4×4 Agent enters in [1,1] 16 rooms Wumpus: A deadly beast who kills anyone entering his room. Pits: Bottomless pits that will trap you forever. Gold

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Wumpus World Agents Sensors: Stench next to Wumpus Breeze next to pit Glitter in square with gold Bump when agent moves into a wall Scream from wumpus when killed Agents actions Agent can move forward, turn left or turn right Shoot, one shot
Wumpus World Performance measure +1000 for picking up gold -1000 got falling into pit -1 for each move -10 for using arrow

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Reasoning in the Wumpus World Agent has initial ignorance about the configuration Agent knows his/her initial location Agent knows the rules of the environment Goal is to explore environment, make inferences (reasoning) to try to find the gold. Random instantiations of this problem used to test agent reasoning and decision algorithms (applications? “intelligent agents” in computer games)
Exploring the Wumpus World [ 1,1] The KB initially contains the rules of the environment. The first percept is [ none, none,none,none,none ], move to safe cell e.g. 2,1

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Exploring the Wumpus World [2,1] = breeze indicates that there is a pit in [2,2] or [3,1], return to [1,1] to try next safe cell
Exploring the Wumpus World [1,2] Stench in cell which means that wumpus is in [1,3] or [2,2] YET … not in [1,1] YET … not in [2,2] or stench would have been detected in [2,1] (this is relatively sophisticated reasoning!)

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Exploring the Wumpus World [1,2] Stench in cell which means that wumpus is in [1,3] or [2,2] YET … not in [1,1] YET … not in [2,2] or stench would have been detected in [2,1] (this is relatively sophisticated reasoning!) THUS … wumpus is in [1,3] THUS [2,2] is safe because of lack of breeze in [1,2] THUS pit in [1,3] (again a clever inference) move to next safe cell [2,2]
Exploring the Wumpus World [2,2] move to [2,3] [2,3] detect glitter , smell, breeze THUS pick up gold THUS pit in [3,3] or [2,4]

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What our example has shown us Can represent general knowledge about an environment by a set of rules and facts Can gather evidence and then infer new facts by combining evidence with the rules The conclusions are guaranteed to be correct if The evidence is correct The rules are correct The inference procedure is correct -> logical reasoning The inference may be quite complex E.g., evidence at different times, combined with different rules, etc
What is a Logic?

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chapter7 - Logic Agents and Propositional Logic CHAPTER 7...

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