# Errata

If you find an error or something you don't understand let us know.

To see what printing a book is, look at the first left-hand-side page with printing on it. (This is the page that contains copyright information and Library of Congress Cataloging-in-Publication Data). At the bottom of this page you will find numbers: 10 9 8 7 6... The last of these numbers specifies which printing you have.

## Errata in third and subsequent printings

• Page 111 Exercise 3.18, "cs486" should be "cs489" and "cs340" should be "cs350".
• Page 153, Figure 4.8. Insert "DX := NDX"  in the "then" part of the "if" statement.

## Errata in first and second printings

### Chapter 1: Computational Intelligence and Knowledge

• Page 6, paragraph 2, "of of" should be "of".

### Chapter 2: A Representation and Reasoning System

• Page 63 Exercise 2.1 (a) should read "Give a model of the knowledge base."

### Chapter 3: Using Definite Knowledge

• Page 77 the query cs_or_math_course(C) should be preceded by "?".
• Page 80 line 9 "is absence" -> "its absence"

### Chapter 4: Searching

• Page 155, end of second last paragraph: "and does it the number of variables" should be "and does it in time linear in the number of variables."

### Chapter 5: Representing Knowledge

• Figure 5.3 (page 176). There should be an arc between datalog and definite clauses (not just an arrowhead).
• Exercise 5.2 (page 196). The c in Fred's representation should be x.

### Chapter 6: Knowledge Engineering

• Page 220 The end-bar for the example should be at the bottom of the page.
• Page 221, first paragraph. "HOW" and "WHY" should be swapped. HOW moves from the root to the leaves, and WHY moves from the leaves to the root of the tree.
• Example 6.14 (page 223). "...they can ask how live(l1)...". The "live" should be "lit".
• Page 230, Sec 6.8. "than is provided by the meta-level, you can't rely on the all" should be "than is provided by the meta-level, you can't rely on all the"

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### Chapter 10: Using Uncertain Knowledge

• Page 348 Sec. 10.2: "$current(w_1)\geq 1.3$ means there are more than $1.3$ amps flowing" should be "$current(w_1)\geq 1.3$ means there are at least $1.3$ amps flowing"
• Page 364 (Sec. 10.3) "Consider the wiring example of Figure \ref{powerl} (page \pageref{powerl}). Whether light $l_1$ is lit depends only on whether there is power in wire $w_0$ and whether light $l_1$ is ok. Other variables, such as the position of switch $s_1$, whether light $l_2$ is lit, or who the Queen of Canada is, are irrelevant. Whether light $l_1$ is lit depends only on whether there is power in wire $w_0$ and whether light $l_1$ is ok." Remove the last sentence.
• Example 10.13 In the sentence crossing pages 364 and 366, w3 should be w0. Thus to affect the light l1, any random variable either needs to affect whether there is power in wire w0 or affect whether light l1 is ok.
• Page 384 "Lets initially assume..." should be "Let's initially assume..."
• Page 389 Sec 10.4 "Lets continue Example ..." should be "Let's continue Example ..."
• Example 10.25 (page 390). (Thanks to Bonnie Webber.) For the case where you check and report and see smoke, 10 should be subtracted from the values. Thus it should read:
E(V | call and check and report and see_smoke) = -210E(V | ¬call and check and report and see_smoke)   = -5010 * P(fire | report and see_smoke) - 10 * P(¬fire | report and see_smoke)   = -5010 * 0.964 - 10 * 0.056   = -4830

### Chapter 11: Learning

• Figure 11.7 (page 413). The error for iteration 80 should be 0.179 (not 0.178).
• Example 11.16 (page 426). "...the probability of observing n A's in m independent trials..." should be "...the probability of observing a particular sequence of n A's in m independent trials...". It is, of course, a particular sequence that will be observed. This isn't the binomial distribution which is the probability of observing any sequence of n A's in m independent trials (for the binomial distribution the number in the book needs to be multiplied by the number of ways you can get n A's in m trials).
• Page 426 (first paragraph after the heading). "P(model|data)=1" should be "P(data|model)=1".
• Example 11.16 (page 427). (Thanks to Bonnie Webber.) This looks as though it has been run using a different database.

Let decision tree d0 be the tree with no internal nodes and predicts read with probability ½ (this is the most likely tree with no internal nodes given the data). Then:

P(data | d0) = ½9 * ½9 = 0.00000149
Let decision tree d1a be the tree that splits on length, such that when length=long it predicts reads with probability 0 and when length=short it predicts reads with probability 9/11.
P(data | d1a) = 17 * (9/11)9 * (2/11)2 = 0.00543
Let decision tree d1b be the tree that splits on thread, such that when thread=new it predicts reads with probability 7/10 (as 7 out of the 10 examples with thread=new have user_action=reads) and when thread=follow_up it predicts reads with probability 2/8.
P(data | d1b) = (7/10)7 * (3/10)3 * (6/8)6 * (2/8)2 =  0.0000247

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### Appendix A: Glossary

• Consistent (p. 465) "can" should be "cannot". A set of beliefs is consistent if false cannot be derived.

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### Appendix C: Some more implemented systems

• Page 509 line 6, "had" should be "has"

Last updated 1 November 1999, David Poole, poole@cs.ubc.ca