diff --git a/README.md b/README.md
index f189312..2613286 100644
--- a/README.md
+++ b/README.md
@@ -18,14 +18,6 @@ To-do items, wanted features, bugs:
   
 - Parametrize gen_twisted_boundary over boundaries and
 do my nested spiral
-- Encode the notions of "generator which transforms an
-existing list of boundaries", "generator which transforms
-another generator"
-- This has a lot of functions parametrized over a lot
-of functions.  Need to work with this somehow.
-- Work directly with lists of boundaries. The only thing
-I ever do with them is apply transforms to all of them, or
-join adjacent ones with corresponding elements.
 - Why do I get the weird zig-zag pattern on the triangles,
 despite larger numbers of them? Is it something in how I
 twist the frames?
@@ -47,3 +39,16 @@ Other notes:
 - Picking at random the diagonal on the quad to triangulate with
   does seem to turn 'error' just to noise, and in its own way this
   is preferable.
+
+# Abstractions
+
+- Encode the notions of "generator which transforms an
+existing list of boundaries", "generator which transforms
+another generator"
+- This has a lot of functions parametrized over a lot
+of functions.  Need to work with this somehow.  (e.g. should
+it subdivide this boundary? should it merge opening/closing
+boundaries?)
+- Work directly with lists of boundaries. The only thing
+I ever do with them is apply transforms to all of them, or
+join adjacent ones with corresponding elements.
diff --git a/examples.py b/examples.py
index eaabb4a..96b167e 100755
--- a/examples.py
+++ b/examples.py
@@ -161,7 +161,17 @@ def twist_nonlinear(dx0 = 2, dz=0.2, count=3, scale=0.99, layers=100):
     return mesh
 
 def twist_from_gen():
-    gen = meshgen.gen_inc_y(meshgen.gen_twisted_boundary())
+    b = numpy.array([
+        [0, 0, 0],
+        [1, 0, 0],
+        [1, 0, 1],
+        [0, 0, 1],
+    ], dtype=numpy.float64) - [0.5, 0, 0.5]
+    b = meshutil.subdivide_boundary(b)
+    b = meshutil.subdivide_boundary(b)
+    b = meshutil.subdivide_boundary(b)
+    bs = [b]
+    gen = meshgen.gen_inc_y(meshgen.gen_twisted_boundary(bs))
     mesh = meshgen.gen2mesh(gen, 100, True)
     return mesh
 
@@ -169,20 +179,21 @@ def twist_from_gen():
 # turn = How many full turns to make in inner twist
 # count = How many inner twists to have
 def twisty_torus(frames = 200, turns = 4, count = 4, rad = 4):
+    b = numpy.array([
+        [0, 0, 0],
+        [1, 0, 0],
+        [1, 0, 1],
+        [0, 0, 1],
+    ], dtype=numpy.float64) - [0.5, 0, 0.5]
+    b = meshutil.subdivide_boundary(b)
+    b = meshutil.subdivide_boundary(b)
+    b = meshutil.subdivide_boundary(b)
+    bs = [b]
     # In order to make this line up properly:
     angle = numpy.pi * 2 * turns / frames
-    gen = meshgen.gen_torus_xy(meshgen.gen_twisted_boundary(count=count, ang=angle), rad=rad, frames=frames)
+    gen = meshgen.gen_torus_xy(meshgen.gen_twisted_boundary(bs=bs, count=count, ang=angle), rad=rad, frames=frames)
     return meshgen.gen2mesh(gen, 0, flip_order=True, loop=True)
 
-# frames = How many step to build this from:
-# turn = How many full turns to make in inner twist
-# count = How many inner twists to have
-def twisty_torus_opt(frames = 200, turns = 4, count = 4, rad = 4):
-    # In order to make this line up properly:
-    angle = numpy.pi * 2 * turns / frames
-    gen = meshgen.gen_torus_xy(meshgen.gen_twisted_boundary(count=count, ang=angle), rad=rad, frames=frames)
-    return meshgen.gen2mesh(gen, 0, flip_order=True, loop=True, join_fn=meshutil.join_boundary_optim)
-
 def main():
     fns = {
         ram_horn: "ramhorn.stl",
diff --git a/meshgen.py b/meshgen.py
index 17acd81..26df4ed 100644
--- a/meshgen.py
+++ b/meshgen.py
@@ -6,32 +6,32 @@ import trimesh
 # Generate a frame with 'count' boundaries in the XZ plane.
 # Each one rotates by 'ang' as it moves by 'dz'.
 # dx0 is center-point distance from each to the origin.
-def gen_twisted_boundary(count=4, dx0=2, dz=0.2, ang=0.1):
-    b = numpy.array([
-        [0, 0, 0],
-        [1, 0, 0],
-        [1, 0, 1],
-        [0, 0, 1],
-    ], dtype=numpy.float64) - [0.5, 0, 0.5]
-    b = meshutil.subdivide_boundary(b)
-    b = meshutil.subdivide_boundary(b)
-    b = meshutil.subdivide_boundary(b)
+def gen_twisted_boundary(bs=None, count=4, dx0=2, dz=0.2, ang=0.1):
+    if bs is None:
+        b = numpy.array([
+            [0, 0, 0],
+            [1, 0, 0],
+            [1, 0, 1],
+            [0, 0, 1],
+        ], dtype=numpy.float64) - [0.5, 0, 0.5]
+        b = meshutil.subdivide_boundary(b)
+        b = meshutil.subdivide_boundary(b)
+        b = meshutil.subdivide_boundary(b)
+        bs = [b]
     # Generate 'seed' transformations:
     xfs = [meshutil.Transform().translate(dx0, 0, 0).rotate([0,1,0], numpy.pi * 2 * i / count)
            for i in range(count)]
     # (we'll increment the transforms in xfs as we go)
     while True:
         xfs_new = []
-        bs = []
         for i, xf in enumerate(xfs):
             # Generate a boundary from running transform:
-            b_i = xf.apply_to(b)
-            bs.append(b_i)
+            bs2 = [xf.apply_to(b) for b in bs]
             # Increment transform i:
             xf2 = xf.rotate([0,1,0], ang)
             xfs_new.append(xf2)
         xfs = xfs_new
-        yield bs
+        yield bs2
 
 # This is to see how well it works to compose generators:
 def gen_inc_y(gen, dy=0.1):