### Mistakes and Typos in How to Design Programs

#### Mistakes:

The third printing of the book may contain the following mistakes. They have been corrected in the on-line version:

1. page 136: ``` (dollar-store? (cons .75 (cons 0.95 (cons .25 empty)))) ``` should be ``` (dollar-store? (cons .75 (cons .95 (cons .25 empty)))) ``` (D. Tucker)
2. page 313: Figure 57 mistakenly states the contract for the built-in sort function as ``` quick-sort : (X X -> boolean) (listof X) -> (listof X) ``` The actual contract is: ``` quicksort : (listof X) (X X -> boolean) -> (listof X) ``` (J. Cone)
3. page 317: Exercise 21.4.5 had to be revised as follows to conform to the interface of the arrow.ss teachpack:

 ```Modify the functions of exercises 21.4.3 and 21.4.4 so that pictures move up and down on a canvas. Modify all definitions so that a shape can also be a line; a line has a start position, an end position, and a color. Define `LUNAR`, a list that sketches a lunar lander picture (see figure 58). The list should consist of rectangles, circles, and lines. Develop the program `lunar-lander`. It places LUNAR at the top of a canvas and then uses the modified functions to move the lander up or down. Use the teachpack arrow.ss to give users control over how fast and when the lunar lander should move: ``` (start 500 100) (draw LUNAR) (control-up-down LUNAR 10 move-lander draw-losh) ``` If time permits, modify the function so that a player can move the lander up, down, left or right. Use `controller` from arrow.ss to control the movements in all directions. ```

Thanks to Dung Nguyen and David Kay, Irvine, CA

The following items correct errors in the first and second printing of the book. They have all been corrected in the third printing of the book and the on-line version.

1. page 24:

The problem statement correctly specifies that "[d]ecreasing the price by a dime (\$.10) increases attendance by 15." Later, the book includes the sentence "The base attendance at a price of five dollars is 120, and for each 15 cents less than five dollars, 10 more attendees show up." This second claim is incorrect.

Thanks to Chuck Floyd, Kerrville, TX

2. page 92 (figure 19)

The book specifies that

```  ;;A shape is either
;;1. a circle, or
;;2. a structure.
```
Naturally, this should be
```  ;;A shape is either
;;1. a circle, or
;;2. a square.
```

Thanks to Jamie Raymond, Houston, TX

3. page 122

The book incorrectly defines our-cons as:

```(define (our-cons a-value a-list) (make-pair a d))
```
It should be
```(define (our-cons a-value a-list) (make-pair a-value a-list))
```

Thanks to Hrvoje Blazevic (Master, LPG/C Harriette N)

4. page 122:
```(define (our-cons a-value a-list)
(cond
[(empty? a-list) (make-pair any a-list)]
[(our-cons? a-list) (make-pair any a-list)]
[else (error 'cons "list as second argument expected")]))
```
should be
```(define (our-cons a-value a-list)
(cond
[(empty? a-list) (make-pair a-value a-list)]
[(our-cons? a-list) (make-pair a-value a-list)]
[else (error 'our-cons "list as second argument expected")]))
```

Thanks to Nguyen Cong Vu, Ho Chi Min City, Viet Nam

5. page 158 (exercise 11.3.1)

The book mistakenly specifies `random` as a function that consumes a natural number. Instead, `random` consumes an integer greater than or equal to 1 (and less than or equal to 2147483647).

Thanks to Marvin D. Hernandez, Miami, FL

6. page 159 (exercise 11.3.2)

The exercise had been misinterpreted twice. The new wording is: and produces a list of that many numbers, each randomly chosen from the range from 20 to 120.

Develop the function `tie-dyed`. It consumes a natural number and produces a list of that many numbers, each randomly chosen in the range from `20` to `120`. Use `tie-dyed` to apply `draw-circles` from exercise~9.5.8.

Thanks to Stephen Bloch, New York, NY

7. pages 172-175

The section switches from the development of a descending sort to that of an ascending sort during the transition from the development of `sort` to the development of `insert`.

Figure 33 (page 175) should be as follows:

 ```;; `sort : list-of-numbers -> list-of-numbers` ;; to create a list of numbers with the same numbers as ;; `alon` sorted in descending order (define (sort alon) (cond [(empty? alon) empty] [(cons? alon) (insert (first alon) (sort (rest alon)))])) ;; `insert : number list-of-numbers (sorted) -> list-of-numbers` ;; to create a list of numbers from `n` and the numbers on ;; `alon` that is sorted in descending order; `alon` is sorted (define (insert n alon) (cond [(empty? alon) (cons n empty)] [else (cond [(>= n (first alon)) (cons n alon)] [(< n (first alon)) (cons (first alon) (insert n (rest alon)))])])) ```

Thanks to Daniel P. Friedman, Bloomington, IN

8. page 174

"make-structure" should be "make-mail".

9. page 182

We have added the following paragraph at the end of the page:

Also, use the Scheme operation `append`, which consumes two lists and produces the concatenation of the two lists. For example:

```  (append (list 'a 'b 'c) (list 'd 'e))
= (list 'a 'b 'c 'd 'e)
```

Thanks to Stephen Bloch, Garden City, NY

10. page 236

``````
(list-pick (cons 'a empty) 3)
;; expected value:
false
```
should be
```
(list-pick (cons 'a empty) 3)
;; expected value:
(error 'list-pick "...")
```
```

Thanks to Hrvoje Blazevic (Master, LPG/C Harriette N)

11. pages 237-241:

Replace all occurrences of ``` (define (list-pick n alos) ```
with ``` (define (list-pick alos n) ```

Thanks to Jesse Janzer and Matthew Litman, Atlanta, GA.

12. pages 240, 241

Replace all occurrences of `false` with ``` (error 'list-pick "list too short") ```

Thanks to Hrvoje Blazevic (Master, LPG/C Harriette N)

13. pages 267

```4.   (+ (local ((define (f x) (g (+ x 1)))
(define (g x y) (+ x y)))
(f 10))
555)
```
should be
```4.   (+ (local ((define (f x) (g (+ x 1) 22))
(define (g x y) (+ x y)))
(f 10))
555)
```

Thanks to Hrvoje Blazevic (Master, LPG/C Harriette N)

14. pages 316, 317: Exercise 21.4.1 should read :
Abstract the functions `draw-a-circle` and `clear-a-circle` into a single function `process-circle`.
Define `translate-circle` using `process-circle`.
Exercise 21.4.2 should read:
Abstract the functions `draw-a-rectangle` and `clear-a-rectangle` into a single function `process-rectangle`.
Define `translate-rectangle` using `process-rectangle`.

Thanks to Hrvoje Blazevic (Master, LPG/C Harriette N)

15. page 319

The definition of `sort` is incorrect. It should be as follows:

 `````` ;; sort : (listof number) -> (listof number) (define (sort a-list) (local ((define (insert an alon) (cond [(empty? alon) (list an)] [else (cond [(> an (first alon)) (cons an alon)] [else (cons (first alon) (insert an (rest alon)))])]))) (reduce empty insert a-list))) ``` ```

Thanks to David Kay, Irvine, CA

16. page 376

The enumerations are missing a number each. Here are the correct versions:

```  1.  18 is evenly divisible by 1, 2, 3, 6, 9, and 18;
2.  24 is evenly divisible by 1, 2, 3, 4, 6, 8, 12, and 24.
```

Thanks to Daniel P. Friedman, Bloomington, IN

17. page 386

The sequence of Bezier images is misleading. Here is an improved version:   18. page 390: Exercise 27.2.3 should read:
Design `file->list-of-checks`. The function consumes a file of numbers and outputs a list of restaurant records.

Thanks to Hrvoje Blazevic (Master, LPG/C Harriette N)

19. page 451

The application of ` make-last-item ` in `invert` receives the arguments in the wrong order:

 ```(define (invert alox) (cond [(empty? alox) empty] [else (make-last-item (first alox) (invert (rest alox)))])) ```

Thanks to Daniel P. Friedman, Bloomington, IN

20. page 404/405: The text states that
"Its solution is x = 2, y = 1, and z = 1"
in reference to the list-specified system of equations. Instead, it should read:
"Its solution is x = 1, y = 1, and z = 1"

Thanks to Hrvoje Blazevic (Master, LPG/C Harriette N)

21. page 432

Figure 81 contains a mistake in the definition of `vector-sum`. Here is the correct version:

 ```;; `vector-sum : (vectorof number) -> number` ;; to compute the sum of the numbers in `v` (define (vector-sum v) (vector-sum-aux v (vector-length v))) ```

Thanks to Nguyen Cong Vu, Open University, Ho Chi Minh City, Viet Nam

22. page 534:

The function definition in exercise 37.2.7 should read as follows:

 ```(define (reveal-list! cw sw guess) (local ((define (reveal-one chosen-letter status-letter) (cond [(symbol=? chosen-letter guess) guess] [else status-letter]))) (set! status-word (map reveal-one cw sw)))) ```

Thanks to Hrvoje Blazevic (Master, LPG/C Harriette N)

23. page 558

In exercise 38.4.3, part 3 the program is illegal in Advanced Scheme. Here is the corrected version:

 ```(define (make-box x) (local ((define contents x) (define (new y) (set! contents y)) (define (peek) contents)) (list new peek))) ```

Thanks to Dung X. Nguyen, Houston, TX.

24. page 564

In exercise 38.4.4 the ` make-box ` function is illegal in Advanced Scheme. Here is the corrected version:

 ```(define (make-box x) (local ((define contents x) (define (new y) (set! contents y)) (define (peek) contents)) (list new peek))) ```

Thanks to Hrvoje Blazevic (Master, LPG/C Harriette N)

25. pages 620, 621:

The contract and header for `count-a-vowel` are repeatedly misstated. Here is the correction:

 ```;; `count-a-vowel : letter (vector number number number number number) -> void` ;; effect: to modify `counts` at the appropriate place if `l` is a vowel, ;; none otherwise (define (count-a-vowel l counts) ...) ```

Thanks to Hrvoje Blazevic (Master, LPG/C Harriette N)

26. page 658:

The definition of `for-interval` should be as follows:

 `````` (define (for-interval i end? step action) (cond [(end? i) (action i)] [else (begin (action i) (for-interval (step i) end? step action)]))) ``` ```

Thanks to Hrvoje Blazevic (Master, LPG/C Harriette N)

#### Typos:

We have also found the following typos:

1. page 7: "lanuages" should be "languages" (D.P. Friedman)
2. page 16: "DrScheme's catches" should be "DrScheme catches" (D.P. Friedman)
3. page 20: "for process" should be "for a process" (D.P. Friedman)
4. page 21: "The `area-of-disk` program ..." should be "The `area-of-ring` program ..." (R. Egli) "for process" should be "for a process" (D.P. Friedman)
5. page 23: `revenue : number number -> number` should be `revenue : number -> number`
6. page 25 (figure 5): replace "attendance" with "attendees" (J. Zachary)
7. page 26: "in the both columns" should be "in both columns" (D.P. Friedman)
8. page 28: "invokes" should be "evokes" (J. Zachary)
9. page 34: 4.2.2 "four" should be "three"
10. page 36: Read: "After clicking the Execute button we can compare the two numbers." (Joe Zachary)
11. page 59: the box should contain '606-7771 in its "phone" compartment (M. D. Hernandez)
12. page 67: superfluous ")" at end of first expected value (M. D. Hernandez)
13. page 81: wrong font for "first" in structure definition (D.P. Friedman)
14. page 84: two extra "}" in the data definition of shape
15. page 86: two extra "}" in the data definition of shape (D. Tucker)
16. page 92: figure 19, right hand column definition of `perimeter-circle` should use `circle-radius` [not `circle-length`] (G. Hosford)
17. page 108: "when we evaluate an the error expression" should be "when we evaluate the error expression" (V. Proulx)
18. page 108: "must look the pragmatics" should be "must look at the pragmatics" (D.P. Friedman)
19. page 119: "juice brie cheese" should be "juice, brie-cheese" (D. Tucker, G. Hosford)
20. page 134: "on on" should be "on" (D.P. Friedman)
21. page 140: "euro accounts" should be "euro amounts"
22. page 143: "a the" should be "the" (D.P. Friedman)
23. page 146: "each objects" should be "each object"
24. page 153: read: "flavors of definitions" (Joe Zachary)
25. page 154: read "A function on natural numbers must extract the number that went into the construction of a positive natural number" (Joe Zachary)
26. page 158: "namers" should be "names" (Joe Zachary)
27. page 159: "The typical riot uses \scheme{'red} only." should be "The typical riot uses \scheme{RED} only."
28. page 159: "Develop the function \scheme{create-prices}, which consumes a natural number and produces a list with a corresponding number of prices between \\$.10 and \\$10.00 with increments of a dime."
29. page 162: "cond-clauses" should be "cond-clause" (Joe Zachary)
30. page 166: ``` (define (tabulate-f-up-to-20 n-above-20) ...) ``` should be ``` (define (tabulate-f-up-to-20 n-below-20) ...) ``` Hrvoje Blazevic
31. page 167, exercise 11.5.2: "Eliminate + from these definitions, too." should be "Eliminate + from this definition, too." (B. Duba)
32. page 169: "means of combining" should be "means combining" (J. Zachary)
33. page 172: "create a sorted list" should be "creates a sorted list" (D.P. Friedman)
34. page 178: "we discuss the first alternative" should be "we discuss the second alternative" (S. Bloch)
35. page 179 (figure 34): ``` (draw-solid-line (first a-poly) (second a-poly) RED) ``` should be ``` (draw-solid-line (first a-poly) (second a-poly) 'red) ``` (J. Raymond)
36. page 192: "conventions concerning on" should be "conventions concerning on" (D.P. Friedman)
37. page 198: "The contracts differ slightly." should be "The results differ slightly." (S. Bloch)
38. page 201: "tha is" should be "that is" (D.P. Friedman)
39. page 202: "larger than 65" should be "larger than 66" (Joe Zachary)
40. page 215: ex 15.1.2: The second sentence should read "It determines how far the first blue-eyed descendant, if one exists, is removed from the given parent." (Sharon Salveter)
41. page 218: "fun-for-parent" should be "fun-parent", "for-for-loc" should be "fun-children" (D.P. Friedman)
42. page 223: "the file named read!" should be "a file named read!" (Joe Zachary)
43. page 225: "directly apply to" should be "directly applies to" (D.P. Friedman)
44. page 227: added "Do not define your own dir structures." to create-dir (Hrvoje Blazevic)
45. page 228: changed "in the content field" to "in a `dir` structure" in 16.3.3 (Hrvoje Blazevic)
46. page 235: "that a natural" should be "that consumes a natural" (D.P. Friedman)
47. page 236: change all occurrences of null? to empty? (Hrvoje Blazevic)
48. page 239: "like list-pick0" should be "like list-pick" (D.P. Friedman)
49. page 240: "consider the second part" should be "consider the first part" (D.P. Friedman)
50. page 244: "data definition data definition" should be "data definition" (D.P. Friedman)
51. page 244: "choses" should be "chooses"
52. page 244: in the three test cases, use `reveal-list` instead of ``` reveal ``` (Hrvoje Blazevic)
53. page 247: "if it the pattern" should be "if the pattern" (D.P. Friedman)
54. page 249: ``` (interpret-with-one-def (substitute val-of-arg fun-para fun-body) a-fun-def) ``` should be ``` (interpret-with-one-def (subst ... ... ...) a-fun-def) ```
55. page 253: "contain the numbers" should be "contain the same numbers" (D.P. Friedman)
56. page 258: "test cases" should be "test" (D.P. Friedman)
57. page 258: In Ex. 17.8.11, "section 17.1" should be "section 17.3" (Jeffere H.)
58. page 259: "a good `local` definitions" should be "a good understanding of `local` definitions" (D.P. Friedman)
59. page 261: "Determine which of the following definitions or expressions is legal and which one is not:" should be "Determine which of the following definitions or expressions are legal and which ones are not:" (D.P. Friedman)
60. page 266: ``` (local ((define (f x) exp-1))) exp) ``` should be ``` (local ((define (f x) exp-1)) exp) ``` (H. Blazevic)
61. page 266: ``` (local ((define PI 3))) exp) ``` should be ``` (local ((define PI 3)) exp) ``` (H. Blazevic)
62. page 263: "f-1' instead of f-11" should be "f-1' instead of f-1" (D.P. Friedman)
63. page 264: "which of y's" should be "which of the y's" (D.P. Friedman)
64. page 264:
```= (define y 10)
(define y1 10)
(define z1 20)
(+ 10 z1)
```
was duplicated (Nguyen Cong Vu)
65. page 269: "lists of records on rock stars" should be "lists of records of rock stars" (Joe Zachary)
66. page 270: "For 'Sean," should be "For 'Wen," (D.P. Friedman)
67. page 273: "in in" should be "in" (D.P. Friedman)
68. page 274: "to write to" should be "to write two" (D.P. Friedman)
69. page 276: "variables, function, and structures" should be "variables, functions, and structures" (Joe Zachary)
70. page 287: ``` (cons 6 empty) ``` should be ``` (cons 4 empty) ``` (H. Blazevic)
71. page 291: "The first variant flattened ..." should be "The first variant flattens ..." (Joe Zachary)
72. page 292: "Test each of them with the following two lists:" should be "Test each of them with the following three lists:" (H. Blazevic)
73. page 295: the foonote was accidentally inlined (D.P. Friedman)
74. page 316: "perparation" should be "preparation"
75. page 324:
`filter2 : (X Y -> boolean) -> (Y (listof X) -> (listof X))`
should be
`filter2 : (X Y -> boolean) -> ((listof X) Y -> (listof X))` (H. Blazevic)
76. page 327: "to obtain obtain" should be "to obtain" (D.P. Friedman)
77. page 328: Here is the correct contract of `draw-message`: `gui-item [message%] string -> true`
`get-text` should be ` text-contents ` (J. Zachary)
78. page 330: "functionq" should be "function" (D.P. Friedman)
79. page 331:
``` (define digit-choosers (build-list 3 (lambda (i) (make-choice DIGITS)))) ```
should be
``` (define digit-choosers (local ((define (builder i) (make-choice DIGITS))) (build-list 3 builder))) ``` (H. Blazevic)
80. page 338: "multiplying a fixed constant wit" should be "multiplying a fixed constant with" (Joe Zachary)
81. page 339: "to add just a few of the first few terms" should be "to add just the first few terms" (D.P. Friedman)
82. page 346: "The teachpack graphing.ss provides two operations for drawing lines: `graph-line`. The operation consumes a line like `y` and a color, say, `RED`."
should be
"The teachpack graphing.ss provides one operation for drawing lines: `graph-line`. The operation consumes a line like `y` and a color, say, `'red`." (Joe Zachary)
83. page 349: "the answer will be depend on e" should be "the answer will depend on e" (H. Blazevic)
84. page 358: "until drops" should be "until it drops off the table" (D.P. Friedman)
85. page 359 (figure 66): the two occurrences of RED should be 'red (H. Blazevic)
86. page 359: "directiones" should be "directions" (J. Zachary)
87. page 369: "howthe it works" should be "how it works" (D.P. Friedman)
88. page 373: "algorith" should be "algorithm"
89. page 379: "wreck" should be "wreak" (J. Zachary)
90. page 393: "Here f(m) > 0," should be "Here f(m) < 0," (H. Blazevic)
91. pages 392-395: "Mean Value Theorem" should be "Intermediate Value Theorem" (B. Richter)
92. page 400: ``` (define (fprime (d/dx f)))) ``` should be ``` (define fprime (d/dx f))) ``` (H. Blazevic)
93. page 405: "2 x + 2 y + z z = 2" should be "2 x + 2 y + z = 2" (H. Blazevic)
94. page 411: ";; to create a path from some node on `lo-originations` to `destination`" should be ";; to create a path from some node on `lo-Os` to `D`" (J. Zachary)
95. page 412: the calculation should read: ``` (find-route 'B 'D Cyclic-graph) = ... (find-route 'B 'D Cyclic-graph) ... = ... (find-route/list (list 'E 'F) 'D Cyclic-graph) ... = ... (find-route 'E 'D Cyclic-graph) ... = ... (find-route/list (list 'C 'F) 'D Cyclic-graph) ... = ... (find-route 'C 'D Cyclic-graph) ... = ... (find-route/list (list 'B 'D) 'D Cyclic-graph) ... = ... (find-route 'B 'D Cyclic-graph) ... = ... ``` (H. Blazevic)
96. page 425: "a functions running time" should be "a function's running time" (D.P. Friedman)
97. page 434 (ex. 29.4.7): The exercise should read: Develop the function `norm`, which consumes a vector of numbers and produces the square root of the sum of the squares of its numbers. (H. Blazevic)
98. page 435: "veloicity" should "velocity" (Nguyen Cong Vu, Open University, Ho Chi Minh City, Viet Nam)
99. page 437: "a vector of the same how-many as" should be "a vector of the same length as" (D.P. Friedman)
100. page 441: "this loss make a" should be "this loss makes a" (D.P. Friedman)
101. page 447: "(rest ag)" should be "(rest sg)" (H. Blazevic)
102. page 457: Exercise 31.3.1 should read
A second difference between the two functions concerns the order of addition. While the original version of sum adds up the numbers from right to left, the accumulator-style version adds them up from left to right.
Furthermore, replace `(sum (g-series 1000))` with `(sum (g-series #i1000))` (H. Blazevic)
103. page 467: "this application `all-blue-eyed-ancestors` loses" should be "this application of `all-blue-eyed-ancestors` loses" (D.P. Friedman)
104. page 474: "for the states we have reach so far" should be" for the states we have reached so far" (D.P. Friedman)
105. page 477: "consume a the board" should be "consume a board" (D.P. Friedman)
106. page 481: "choice is to round the number and to the closest representable equivalent" should be "choice is to round the number to the closest representable equivalent" (D.P. Friedman)
107. page 498: ``` (set! (if z x y) 5) ``` should be ``` (set! (z x y) 5) ``` (H. Blazevic)
108. page 504: "a variable `define`d at top-level variable" should be "a variable `define`d at top-level" (D.P. Friedman)
109. page 504: "Supposed we evaluate" should be "Suppose we evaluate" (D.P. Friedman)
110. page 517: "whether the functions has the desired result" should be "the function has the desired result and effect" (D.P. Friedman)
111. page 517: "efffects" should be "effects"
112. page 518: "a particular good one" should be "a particularly good one" (D.P. Friedman)
113. page 523 (figure 103): "check-guess" should be "check-color" (H. Blazevic)
114. page 528: "Thus, the matching action is a build a word as long as `chosen-word` but to use `'_` as the letters." should be "Thus, the matching action is to build a word as long as `chosen-word` from `'_`. (D.P. Friedman)
115. pages 536/537: `chosen-wor` should be `chosen-word` (D.P. Friedman)
116. page 566: "Alonzo Church in the last 1920s as follows:" should be "Alonzo Church in the late 1920s as follows:" (D.P. Friedman)
117. page 575: The last line of the definition of `next-color` requires a closing ")". (D. Smith)
118. page 577: This sets the light at `'sunrise@cmu` to green. (H. Blazevic)
119. page 595 "in the structure name p" should be "in the structure named p" (D.P. Friedman)
120. page 603: ``` (define (board-set! a-board i j) ...) ``` should be ``` (define (board-flip! a-board i j) ...) ``` (H. Blazevic)
121. page 616 "a self-referential descriptions" should be "a self-referential description" (D.P. Friedman)
122. page 616: ``` reset : -> true ``` should be ``` reset : -> void ``` (H. Blazevic)
123. page 625: "`hand0` becomes a card with two hands" should be "`hand0` becomes a hand with two cards" (H. Blazevic)
124. page 629: "preceeds" should be "precedes" (D.P. Friedman)
125. page 631 `(sorted-insert! 1 CLUBS hand0)` should be `(sorted-insert! 2 CLUBS hand0)` (D.P. Friedman)
126. page 634: the last line of figure 124, "`manage`))" should be "`service-manager`))"

Furthermore, the defininition of `service-manager` should be:

``````
(define (service-manager msg)
(cond
[(symbol=? msg 'insert!)
(lambda (r s)
(cond
[(> r (hand-rank the-hand))
(set! the-hand (make-hand r s the-hand))]
[else (insert-aux! r s the-hand)]))]
[else (error 'managed-hand "message not understood")]))
```
```
(H. Blazevic)
127. page 635: "determing" should be "determining" (D.P. Friedman)
128. page 636: "structure-mutating the functions" should be "structure-mutating functions" (D.P. Friedman)
129. page 637: "`equal-posn?: posn posn -> boolean`" should be "`equal-posn : posn posn -> boolean`" (H. Blazevic)
130. page 639: ```;; eq-posn? : posn posn -> boolean ;; to determine whether two posn structures ;; are affected by the same mutation (define (equal-posn p1 p2) ...) ``` should be ```;; eq-posn : posn posn -> boolean ;; to determine whether two posn structures ;; are affected by the same mutation (define (eq-posn p1 p2) ...) ```

"``` (define (equal-posn p1 p2) ```" should be " ``` (define (eq-posn p1 p2) ``` "

(H. Blazevic)

131. page 640: " ``` (define (equal-posn p1 p2) ``` " should be " ``` (define (eq-posn p1 p2) ``` "

`equal-posn` should always be `eq-posn `

``````;; eq-posn? : posn posn -> boolean
;; to determine whether two posn structures
;; are affected by the same mutation
(define (equal-posn p1 p2) ...)
``````
``` ``` should be ```;; eq-posn : posn posn -> boolean ;; to determine whether two posn structures ;; are affected by the same mutation (define (eq-posn p1 p2) ...) ``` (H. Blazevic)

132. page 641: ex. 42.2.1 eq-posn? should be eq-posn (H. Blazevic)
133. page 655: ```(define (partition V left right) (local ((define pivot-position left) (define the-pivot (vector-ref V left)) (define (partition-aux left right) (local ((define new-right (find-new-right V the-pivot right left)) (define new-left (find-new-left V the-pivot left right))) ... ))) (partition left right))) ``` should be ```(define (partition V left right) (local ((define pivot-position left) (define the-pivot (vector-ref V left)) (define (partition-aux left right) (local ((define new-right (find-new-right V the-pivot left right)) (define new-left (find-new-left V the-pivot left right))) ... ))) (partition-aux left right))) ``` (H. Blazevic)

134. page 656 (figure 131): ```(define (partition V left right) (local ((define pivot-position left) (define the-pivot (vector-ref V left)) (define (partition-aux left right) (local ((define new-right (find-new-right V the-pivot right left)) (define new-left (find-new-left V the-pivot left right))) (cond [(>= new-left new-right) (begin (swap V pivot-position new-right) new-right)] [else (begin (swap V new-left new-right) (partition-aux new-left new-right))])))) (partition-aux left right))) ``` should be ```(define (partition V left right) (local ((define pivot-position left) (define the-pivot (vector-ref V left)) (define (partition-aux left right) (local ((define new-right (find-new-right V the-pivot left right)) (define new-left (find-new-left V the-pivot left right))) (cond [(>= new-left new-right) (begin (swap V pivot-position new-right) new-right)] [else ; (< new-left new-right) (begin (swap V new-left new-right) (partition-aux new-left new-right))])))) (partition-aux left right))) ``` (H. Blazevic)

135. page 658: `(list 1.10 329/300 328/300)` should be ``` (list 1.10 329/300 82/75) ``` (H. Blazevic)
136. page 660: "related with each other" should be "related to each other" (D.P. Friedman)
137. page 670: "cannot possible produce" should be "cannot possibly produce" (D.P. Friedman)
138. page 678: "extrance" should be "entrance"

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