diff --git a/ch_1_intro.md b/ch_1_intro.md
index 958cca3..4b222cb 100644
--- a/ch_1_intro.md
+++ b/ch_1_intro.md
@@ -876,8 +876,10 @@ Here is the finished `cngon!`:
```
fn cngon! (n, radius) -> {
- let angle = sub (inv (2), inv (n))
+ let angle = add (inv (4), inv (mult (2, n)))
+ & ^... this is equation (5), above, solving for `d`
let edge = mult (2, radius, sin (inv (mult (2, n))))
+ & ^... this is equation (8), above, solving for `e`
penup! ()
forward! (radius)
@@ -918,7 +920,13 @@ Combine the ideas of `spingon!` with your newly constructed `cngon!`.
Design a fancier `cngon!` that fills up a polygon with textures.
Here are a few visual tips for Exercises 1.3 and 1.4:
-{{Figure 13: `spincngon`s. Bottom of p. 32.}}
+
+
+
+
+
+
+
+
+fn ngon! (n, edge) -> {
+ repeat n {
+ forward! (edge)
+ right! (inv (n))
+ }
+}
+
+fn cngon! (n, radius) -> {
+ let angle = add (inv (4), inv (mult (2, n)))
+ let edge = mult (2, radius, sin (inv (mult (2, n))))
+
+ penup! ()
+ forward! (radius)
+ right! (angle)
+ pendown! ()
+ ngon! (n, edge)
+ left! (angle)
+ penup! ()
+ back! (radius)
+ pendown! ()
+}
+
+fn twisty_nonagons! (times, iter, radius, growth) -> {
+ if gte? (iter, times) then :ok
+ else {
+ cngon! (9, radius)
+ right! (inv (times))
+ twisty_nonagons! (times, inc (iter), add (radius, growth), growth)
+ }
+}
+
+& twisty_nonagons! (10, 0, 100, 3)
+
+fn centre_squares! (times, radius, growth) -> {
+ if lt? (times, 1) then :ok
+ else {
+ cngon! (4, radius)
+ centre_squares! (dec (times), add (radius, growth), growth)
+ }
+}
+
+right! (0.125)
+centre_squares! (10, 100, 4)
+
+fn twisty_triangles! (times, radius, angle, growth) -> {
+ if lt? (times, 1) then :ok
+ else {
+ cngon! (3, radius)
+ right! (angle)
+ twisty_triangles! (dec (times), sub (radius, growth), angle, growth)
+ }
+}
+
+& right! (inv (6))
+& twisty_triangles! (8, 100, inv (120), 10)
+
+hideturtle! ()
+
+
+
+
diff --git a/fig_13.2.svg b/fig_13.2.svg
new file mode 100644
index 0000000..9fa5886
--- /dev/null
+++ b/fig_13.2.svg
@@ -0,0 +1,251 @@
+
+
+
+
+
+
+
+
+
+fn ngon! (n, edge) -> {
+ repeat n {
+ forward! (edge)
+ right! (inv (n))
+ }
+}
+
+fn cngon! (n, radius) -> {
+ let angle = add (inv (4), inv (mult (2, n)))
+ let edge = mult (2, radius, sin (inv (mult (2, n))))
+
+ penup! ()
+ forward! (radius)
+ right! (angle)
+ pendown! ()
+ ngon! (n, edge)
+ left! (angle)
+ penup! ()
+ back! (radius)
+ pendown! ()
+}
+
+fn twisty_nonagons! (times, iter, radius, growth) -> {
+ if gte? (iter, times) then :ok
+ else {
+ cngon! (9, radius)
+ right! (inv (times))
+ twisty_nonagons! (times, inc (iter), add (radius, growth), growth)
+ }
+}
+
+twisty_nonagons! (10, 0, 100, 3)
+
+fn centre_squares! (times, radius, growth) -> {
+ if lt? (times, 1) then :ok
+ else {
+ cngon! (4, radius)
+ centre_squares! (dec (times), add (radius, growth), growth)
+ }
+}
+
+& right! (0.125)
+& centre_squares! (10, 100, 4)
+
+fn twisty_triangles! (times, radius, angle, growth) -> {
+ if lt? (times, 1) then :ok
+ else {
+ cngon! (3, radius)
+ right! (angle)
+ twisty_triangles! (dec (times), sub (radius, growth), angle, growth)
+ }
+}
+
+& right! (inv (6))
+& twisty_triangles! (8, 100, inv (120), 10)
+
+hideturtle! ()
+
+
+
+
diff --git a/fig_13.3.svg b/fig_13.3.svg
new file mode 100644
index 0000000..1cbbadb
--- /dev/null
+++ b/fig_13.3.svg
@@ -0,0 +1,118 @@
+
+
+
+
+
+
+
+
+
+fn ngon! (n, edge) -> {
+ repeat n {
+ forward! (edge)
+ right! (inv (n))
+ }
+}
+
+fn cngon! (n, radius) -> {
+ let angle = add (inv (4), inv (mult (2, n)))
+ let edge = mult (2, radius, sin (inv (mult (2, n))))
+
+ penup! ()
+ forward! (radius)
+ right! (angle)
+ pendown! ()
+ ngon! (n, edge)
+ left! (angle)
+ penup! ()
+ back! (radius)
+ pendown! ()
+}
+
+fn twisty_nonagons! (times, iter, radius, growth) -> {
+ if gte? (iter, times) then :ok
+ else {
+ cngon! (9, radius)
+ right! (inv (times))
+ twisty_nonagons! (times, inc (iter), add (radius, growth), growth)
+ }
+}
+
+& twisty_nonagons! (10, 0, 100, 3)
+
+fn centre_squares! (times, radius, growth) -> {
+ if lt? (times, 1) then :ok
+ else {
+ cngon! (4, radius)
+ centre_squares! (dec (times), add (radius, growth), growth)
+ }
+}
+
+& right! (0.125)
+& centre_squares! (10, 100, 4)
+
+fn twisty_triangles! (times, radius, angle, growth) -> {
+ if lt? (times, 1) then :ok
+ else {
+ cngon! (3, radius)
+ right! (angle)
+ twisty_triangles! (dec (times), sub (radius, growth), angle, growth)
+ }
+}
+
+right! (inv (6))
+twisty_triangles! (8, 100, inv (120), 10)
+hideturtle! ()
+
+
+
+
+
+
+
+
+
+##### Figure 13: `spincngon`s.
#### Exercise 1.5
Design a Ludus function that puts polygons on the vertices of other polygons.
diff --git a/fig_13.1.svg b/fig_13.1.svg
new file mode 100644
index 0000000..9b33e85
--- /dev/null
+++ b/fig_13.1.svg
@@ -0,0 +1,151 @@
+
+
+
diff --git a/fig_13.2.svg b/fig_13.2.svg
new file mode 100644
index 0000000..9fa5886
--- /dev/null
+++ b/fig_13.2.svg
@@ -0,0 +1,251 @@
+
+
+
diff --git a/fig_13.3.svg b/fig_13.3.svg
new file mode 100644
index 0000000..1cbbadb
--- /dev/null
+++ b/fig_13.3.svg
@@ -0,0 +1,118 @@
+
+
+