Problem 4c.

command roundthing
{
   antialias 100
   load dbngraphics.dbn
   paper 12
   repeat x 0 36
   {
      circle 48 60 x (x*x*x/36-48)
   }
}

command triangle a b c
{
   repeat e 0 c
   {
      pen (c/2-e)
      smaller? (c/2) e
      {
         pen (e-c/2)
      }
      line (a+e) b (a+c/3) (b+2*c/5)
   }
}

command square a b c
{
   line a b (a + c) b
   line (a + c) b (a + c) (b - c)
   line (a + c) (b - c) a (b - c)
   line a (b - c) a b
}

roundthing
repeat k 13 1

{
   triangle (2*k) (k*k*k/90) (k*k)
}

pen 80
square 60 40 45
square 20 80 85

-gary escudero