How To Fold It:

by Joseph O'Rourke 
I would like to thank Ryuhei Uehara at JAIST, who made many corrections as he translated the book to Japanese.
Chap 
Page 
Location 
Old 
New 
Explanation 
Corrector 
Date 

Preface 
ix 
Lines +1, +5, +6 
64 straight scissors cuts ... 16 stright snips of the scissors rather than 64  70 straight scissors cuts ... 18 straight snips of the scissors rather than 70  The exact count depends a bit on what it means to "cut out" the dolls, and whether or not you take some shortcuts, e.g., but cutting the bottom of their feet separately or as a unit. There are 70 straight segments (18+17+17+18), so cutting each separately uses that many cuts. After folding, 18 suffice to cut out the pattern, which is just a bit over 1/4.  Peter Landweber; JOR 
24 Aug 2011 
1 
18 
Exer. 1.6, Line2 
My answer is incorrect. See below.  Charles W. Wampler 
21 Aug 2011 

Answers to Exer 
152 
Ans. to Exer. 1.6, Line3 
All the points on the circle of radius 2=1+2=3 can only be reached by forming a zigzag with the 2nd link opposing the 1st and 3rd.  [The claim in that sentence is false and should be removed.]  The only points reached uniquely by an nlink robot arm are those on the outer and inner boundary of the reachability annulus—in this case, the circle of radius 5. The points on the circle of radius 3 can be reached by a continuum of configurations of the three links.  Charles W. Wampler 
21 Aug 2011 
Chap 
Page 
Location 
Old 
New 
Explanation 
Corrector 
Date 

1 
6 
Line3 
n > 1  n > 2  Better, as n=2 has already been checked..  Ryuhei Uehara 
20 Jan 2012 
1 
9 
Box 1.3, last sentence of 1st para. 
The length of these vectors is exactly the link length which they "span,"  The lengths of these vectors are exactly the link lengths which they "span,"  Singular→plural  Ryuhei Uehara 
24 Dec 2011 
1 
13 
Last para. 
Should be indented because it is part of Case 2.  Ryuhei Uehara 
24 Dec 2011 

1 
20 
Line7 
(Ruler Folding)  Ruler Folding  Remove parentheses.  Ryuhei Uehara 
24 Dec 2011 
2 
36 
Line+4 
any  any  Italics→underline (for typographical consistency)  Ryuhei Uehara 
24 Dec 2011 
2 
37 
Line+2 of bottom "Open Subproblem" box 
Are there a planar linkages  Are there planar linkages  Typo.  Peter Landweber 
24 Aug 2011 
3 
41 
Line+5 of middle para. 
the purely geometric motion of  the purely geometric notion of  Typo.  Peter Landweber 
24 Aug 2011 
3 
41 
Line4 
3 x 36 = 108 links  3 x 36  1 = 107 links  Mental typo.  Ryuhei Uehara 
20 Jan 2012 
3 
46 
Line14 
established for n=1,2,...,n1  established for 1,2,...,n1  Clearer.  Ryuhei Uehara 
24 Dec 2011 
3 
47 
Line14 
induction hypothesis covers all n up to n1  induction hypothesis covers all values up to n−1  Clearer.  Ryuhei Uehara 
24 Dec 2011 
3 
54 
Fig. 3.16(b) 
label v_{0} on red portion of linkage  Label should be instead v_{5}  Typo.  Peter Landweber 
24 Aug 2011 
4 
57 
Line3 
(Memory aide: red sunset  (Memory aid: red sunset  Typo.  Peter Landweber 
24 Aug 2011 
4 
64 
Line6 & 2 of (blue) Box 4.2 
V · 360° = (M + V) 180° 2 V = M + V or M  V = 0 
V · 360° = (M + V  2) 180° 2 V = M + V  2 or M  V = 2 
Mental typos.  William Lee 
22 Jun 2011 
4 
66 
θ Equation 
θ_{2} + ... θ_{n} = 360°  θ_{2} + ... + θ_{n} = 360°  Add + before θ_{n}  Ryuhei Uehara 
24 Dec 2011 
4 
69 
Line+6 of Sec.4.6.2 
(NPcomplete or worse)  (NPcomplete)  It cannot be worse, because there is a polynomiallength witness for an instance of map folding.  Ryuhei Uehara 
20 Jan 2012 
5 
76 
Exer. 5.2 
for the rectangle  for the rectangle.  Period missing at end of sentence.  Ryuhei Uehara 
24 Dec 2011 
5 
76 
Line2 
see Figure 5.7(a)  see Figure 5.7(a).  Period missing at end of sentence.  Ryuhei Uehara 
24 Dec 2011 
5 
80 
Fig. 5.11(c) 
One red crease should be green.  ~Typo.  MathFest 2011 Minicourse participants 
5 Aug 2011 

5 
82 
Fig.5.13 caption 
Fold andOneCut  Fold and OneCut  Remove extra hyphen.  Ryuhei Uehara 
24 Dec 2011 
5 
91 
Line2 of Sec. 6.2.1 
Figure 6.7(b)  Figure 6.8(b)  Typo.  Ryuhei Uehara 
24 Dec 2011 
6 
94 
Fig.6.13 caption 
0 < θ < 180°  0° < θ < 180°  Add ° for consistency.  Ryuhei Uehara 
24 Dec 2011 
7 
101 
Line9 
truncated icosahedron  truncated icosahedron  Italicize.  Ryuhei Uehara 
24 Dec 2011 
7 
106 
Line+1 
Exercise 6.3[a]  Exercise 6.3(a)  Typo.  Ryuhei Uehara 
24 Dec 2011 
7 
110 
Exer. 7.3 
(Understanding)  (Understanding)  Boldface for consistency.  Ryuhei Uehara 
20 Jan 2012 
7 
113 
Line+4 
all but one edge of A is cut  all but one edge of A are cut  Singular→plural  Ryuhei Uehara 
24 Dec 2011 
7 
115 
Exer. 7.6 
Shortest Paths on Cube.  Shortest Paths on Cube.  Boldface→italics (for typographical consistency)  Ryuhei Uehara 
20 Jan 2012 
9 
135 
Line+4 
Another Alexandrov folding  Another Alexandrov gluing  For consistency.  Ryuhei Uehara 
4 Feb 2012 
9 
135 
Line9 
convex polygon (Recall...  convex polygon. (Recall...  Period missing.  Ryuhei Uehara 
4 Feb 2012 
9 
135 
Line5 
Take any convex polygon  Take any convex polygon P  Better to name it P.  Ryuhei Uehara 
4 Feb 2012 
Answers to Exer 
158 
Ans. to Exer. 3.5, Line+1 
the middle three links  the middle two links  Typo.  Ryuhei Uehara 
8 May 20121 
Answers to Exer 
159 
Ans. to Exer. 4.2, Line2 
leads one of the  leads to one of the  Typo.  Peter Landweber 
24 Aug 2011 
Answers to Exer

160 
Fig.Ans.15 
Row 1, Columns 3 & 4 images  3412: Arrows for 1 and 2 were reversed. 4123: The fold connection between 2 and 3 was missing. 
Ryuhei Uehara 
4 Feb 2012 

Answers to Exer

161 
Fig.Ans.16 
(a) Green line x to AC  Green line should be from x to C.  Ryuhei Uehara 
8 May 2012 

Answers to Exer

162 
Line+3 
will cut out two squares  will cut out a square and a rectangle  In general, the second hole is a rectangle.  Ryuhei Uehara 
4 Feb 2012 
Answers to Exer

166 
Line2 
every tree of n vertices has n edges  every tree of n vertices has n1 edges  Mental typo!  Ryuhei Uehara 
4 Feb 2012 