Cs621 artificial intelligence
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CS621: Artificial Intelligence. Pushpak Bhattacharyya CSE Dept., IIT Bombay Lecture 35–Himalayan Club example; introducing Prolog. Himalayan Club example. Introduction through an example (Zohar Manna, 1974):

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CS621: Artificial Intelligence

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Cs621 artificial intelligence

CS621: Artificial Intelligence

Pushpak BhattacharyyaCSE Dept., IIT Bombay

Lecture 35–Himalayan Club example; introducing Prolog


Himalayan club example

Himalayan Club example

  • Introduction through an example (Zohar Manna, 1974):

    • Problem: A, B and C belong to the Himalayan club. Every member in the club is either a mountain climber or a skier or both. A likes whatever B dislikes and dislikes whatever B likes. A likes rain and snow. No mountain climber likes rain. Every skier likes snow. Is there a member who is a mountain climber and not a skier?

  • Given knowledge has:

    • Facts

    • Rules


Example contd

Example contd.

  • Let mc denote mountain climber and sk denotes skier. Knowledge representation in the given problem is as follows:

    • member(A)

    • member(B)

    • member(C)

    • ∀x[member(x) → (mc(x) ∨ sk(x))]

    • ∀x[mc(x) → ~like(x,rain)]

    • ∀x[sk(x) → like(x, snow)]

    • ∀x[like(B, x) → ~like(A, x)]

    • ∀x[~like(B, x) → like(A, x)]

    • like(A, rain)

    • like(A, snow)

    • Question: ∃x[member(x) ∧ mc(x) ∧ ~sk(x)]

  • We have to infer the 11th expression from the given 10.

  • Done through Resolution Refutation.


Club example inferencing

Club example: Inferencing

  • member(A)

  • member(B)

  • member(C)

    • Can be written as


Cs621 artificial intelligence

  • Negate–


Cs621 artificial intelligence

  • member(A)

  • member(B)

  • member(C)

  • Now standardize the variables apart which results in the following


Cs621 artificial intelligence

10

7

12

5

4

13

14

2

11

15

16

13

2

17


Assignment

Assignment

  • Prove the inferencing in the Himalayan club example with different starting points, producing different resolution trees.

  • Think of a Prolog implementation of the problem

  • Prolog Reference (Prolog by Chockshin & Melish)


Prolog

Prolog


Introduction

Introduction

  • PROgramming in LOGic

  • Emphasis on what rather than how

Problem in Declarative Form

LogicMachine

Basic Machine


Prolog s strong and weak points

Prolog’s strong and weak points

  • Assists thinking in terms of objects and entities

  • Not good for number crunching

  • Useful applications of Prolog in

    • Expert Systems (Knowledge Representation and Inferencing)

    • Natural Language Processing

    • Relational Databases


A typical prolog program

A Typical Prolog program

Compute_length ([],0).

Compute_length ([Head|Tail], Length):-

Compute_length (Tail,Tail_length),

Length is Tail_length+1.

High level explanation:

The length of a list is 1 plus the length of the tail of the list, obtained by removing the first element of the list.

This is a declarative description of the computation.


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