CHAPTER 6 TWO-COLORED WALLPAPER PATTERNS 6.0 ...

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Fig. 6.53 p b ′ 1g → p b ′ 2 6.6.2 Only three types indeed! Looking at the pgg-like patterns obtained so far, we notice that none of them has glide reflection of both kinds in the same direction: such a situation is indeed impossible because of what figures 6.54 & 6.55 tell us: Fig. 6.54
This is a demonstration of a significant fact: the combination of two perpendicular glide reflections (mapping A to B and B to C) produces a half turn (mapping A to C)! We will go through a rigorous proof of a generalization of this in section 7.10, but you should try to verify an important aspect of this new theorem: depending on which way the gliding vector of each of the two glide reflections goes (north-south versus south-north and west-east versus eastwest), as well as the order in which the two glide reflections are combined, we get four plausible centers (and half turns) out of eight actual possibilities; in our case, a ‘symbolic’ rule yields (west-east) × (north-south) = northeast. (Notice also that the distances of the rotation center from the glide reflection axes are equal to half the length of the corresponding gliding vectors; as an important special case, the composition of two perpendicular reflections is a half turn centered at their intersection point. These facts throw new light into sections 2.6 (pma2 border patterns) and 2.7 (pmm2 border patterns), as well as several sections in chapter 4!) Now figure 6.55, together with the preceding remarks, shows why color-preserving and color-reversing glide reflection axes of a pgg-like pattern cannot coexist in the same direction: Fig. 6.55
Page 1 and 2: © 2006 George Baloglou first draft
Page 3 and 4: Fig. 6.3 In the pattern of figure 6
Page 5 and 6: 6.0.4 Symmetry plans and types. Tri
Page 7 and 8: 6.1.2 Infinitely many color-reversi
Page 9 and 10: otations of both kinds, the corresp
Page 11 and 12: eversing 90 0 rotation -- not to me
Page 13 and 14: Fig. 6.13 In view of these facts, t
Page 15 and 16: Fig. 6.15 pg → pm All reflections
Page 17 and 18: Fig. 6.18 pg′ → pm′ All refle
Page 19 and 20: produced six pm-like two-colored wa
Page 21 and 22: 6.3.4 Translations and hidden glide
Page 23 and 24: 6.4 cm types (cm, cm′ , p c ′ g
Page 25 and 26: Fig. 6.28 pm′ → cm′ Fig. 6.29
Page 27 and 28: Fig. 6.31 p b ′ 1 Fig. 6.32 p b
Page 29 and 30: So, while our first two colorings i
Page 31 and 32: pattern ‘look the same’. It’s
Page 33 and 34: p c ′ g p c ′ m R P R P R P R P
Page 35 and 36: Fig. 6.42 pg′ → p2′ Fig. 6.43
Page 37 and 38: proof will be given in section 7.6.
Page 39 and 40: Fig. 6.48 pg → pgg Fig. 6.49 pg
Page 41: So far so good: we obtained four tw
Page 45 and 46: pg′ g ′ pgg′ pgg′ Fig. 6.56
Page 47 and 48: You should compare these pgg symmet
Page 49 and 50: Fig. 6.61 pg → pmg Fig. 6.62 pg
Page 51 and 52: last two types, offspring of p b
Page 53 and 54: Fig. 6.68 p b ′ mg 6.7.4 Symmetry
Page 55 and 56: Fig. 6.70 pmg → pmm Somewhat conf
Page 57 and 58: The two patterns in figures 6.72 &
Page 59 and 60: Fig. 6.77 p b ′ mm → c′ mm Wh
Page 61 and 62: p b ′ gm p b ′ mm p b ′ gm Fi
Page 63 and 64: Fig. 6.80 pmg → pmm → cmm Fig.
Page 65 and 66: Fig. 6.84 p b ′ gg → p b ′ gm
Page 67 and 68: Due to not-that-obvious color incon
Page 69 and 70: p c ′ mm p c ′ mg cm′ m ′ F
Page 71 and 72: Fig. 6.93 pm′ Fig. 6.94 cmm′
Page 73 and 74: Fig. 6.97 p b ′ gm You should be
Page 75 and 76: 6.10 p4 types (p4, p4′ , p c ′
Page 77 and 78: Fig. 6.101 p4′ Fig. 6.102 p c ′
Page 79 and 80: 6.10.5 Symmetry plans. We use ‘st
Page 81 and 82: twofold rotation at C, must both be
Page 83 and 84: p4g p4′ g ′ m p4g′ m ′ p4
Page 85 and 86: Fig. 6.111 We see that the p4m may
Page 87 and 88: Fig. 6.113 pm′ m ′ 2 → p4m′
Page 89 and 90: 6.12.3 Further examples. Our ‘tri
Page 91 and 92: consistent with color! As a consequ
Page 93 and 94:
Predictably, fourfold centers prese
Page 95 and 96:
must have the same effect on color
Page 97 and 98:
Fig. 6.124 p31m′ 6.15 p3m1 types
Page 99 and 100:
Fig. 6.126 p3m′
Page 101 and 102:
p3m1 types. They are not that cruci
Page 103 and 104:
and dots, respectively): Fig. 6.129
Page 105 and 106:
6.17 p6m types (p6m, p6′ mm′ ,
Page 107 and 108:
at the intersection of two reflecti
Page 109 and 110:
Fig. 6.136 p6m′ m ′ In this exa
Page 111 and 112:
Finally, some triangles inside the
Page 113 and 114:
6.18 All sixty three types together
Page 115 and 116:
cm cm′ p c ′ g p c ′ m (II) 1
Page 117 and 118:
cmm cm′ m ′ cmm′ p c ′ mm p
Page 119 and 120:
p4m p4′ mm′ p4′ m ′ m p4m
Page 121:
p6m p6′ m ′ m p6m′ m ′ p6
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CHAPTER 6 TWO-COLORED WALLPAPER PATTERNS 6.0 ...

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