Implementation [of geometric substitution systems]

The most convenient approach is to represent each pattern by a list of complex numbers, with the center of each square being given in terms of each complex number z by {Re[z], Im[z]}. The pattern after n steps is then given by Nest[Flatten[f[#]] &, {0}, n], where for the rule on page 189 f[z_] = 1/2 (1 - ) {z + 1/2, z - 1/2} (f[z_] = (1 - ){z + 1, z} gives a transformed version). For the rule on page 190, f[z_] = 1/2 (1 - ) { z + 1/2, z - 1/2}. For rules (a), (b) and (c) (Koch curve) on page 191 the forms of f[z_] are respectively:

(0.296 - 0.57 ) z - 0.067 - {1.04, 0.237}

N[1/40 {17 (√3 - ) z, -24 + 14 z}]

N[(1/2 (1/√3 - 1)( + {1, -1}) - - (1 + {, -}/√3) z)/2]