diff --git a/arrays.scad b/arrays.scad
index be3bd7c..74d2ea90 100644
--- a/arrays.scad
+++ b/arrays.scad
@@ -424,8 +424,9 @@ function repeat(val, n, i=0) =
 //   list = count(n, [s], [step], [reverse]);
 // Description:
 //   Creates a list of `n` numbers, starting at `s`, incrementing by `step` each time.
+//   You can also pass a list for n and then the length of the input list is used.  
 // Arguments:
-//   n = The length of the list of numbers to create.
+//   n = The length of the list of numbers to create, or a list to match the length of
 //   s = The starting value of the list of numbers.
 //   step = The amount to increment successive numbers in the list.
 //   reverse = Reverse the list.  Default: false.
@@ -435,7 +436,8 @@ function repeat(val, n, i=0) =
 //   nl3 = count(4,3,2);  // Returns: [3,5,7,9]
 //   nl4 = count(5,reverse=true);    // Returns: [4,3,2,1,0]
 //   nl5 = count(5,3,reverse=true);  // Returns: [7,6,5,4,3]
-function count(n,s=0,step=1,reverse=false) = reverse? [for (i=[n-1:-1:0]) s+i*step]
+function count(n,s=0,step=1,reverse=false) = let(n=is_list(n) ? len(n) : n)
+                                             reverse? [for (i=[n-1:-1:0]) s+i*step]
                                                     : [for (i=[0:1:n-1]) s+i*step];
 
 
diff --git a/paths.scad b/paths.scad
index 40159bc..74451c8 100644
--- a/paths.scad
+++ b/paths.scad
@@ -441,7 +441,7 @@ function resample_path(path, N, spacing, closed=false) =
 // Usage:
 //   bool = is_path_simple(path, [closed], [eps]);
 // Description:
-//   Returns true if the path is simple, meaning that it has no self-intersections.
+//   Returns true if the given 2D path is simple, meaning that it has no self-intersections.
 //   Repeated points are not considered self-intersections: a path with such points can
 //   still be simple.  
 //   If closed is set to true then treat the path as a polygon.
@@ -450,6 +450,7 @@ function resample_path(path, N, spacing, closed=false) =
 //   closed = set to true to treat path as a polygon.  Default: false
 //   eps = Epsilon error value used for determine if points coincide.  Default: `EPSILON` (1e-9)
 function is_path_simple(path, closed=false, eps=EPSILON) =
+    assert(is_path(path, 2),"Must give a 2D path")
     [for(i=[0:1:len(path)-(closed?2:3)])
          let(v1=path[i+1]-path[i],
              v2=select(path,i+2)-path[i+1],
diff --git a/regions.scad b/regions.scad
index 3f0a4c5..6777abb 100644
--- a/regions.scad
+++ b/regions.scad
@@ -688,10 +688,11 @@ function _point_dist(path,pathseg_unit,pathseg_len,pt) =
 //   offsetpath = offset(path, [r|delta], [chamfer], [closed], [check_valid], [quality])
 //   path_faces = offset(path, return_faces=true, [r|delta], [chamfer], [closed], [check_valid], [quality], [firstface_index], [flip_faces])
 // Description:
-//   Takes an input path and returns a path offset by the specified amount.  As with the built-in
+//   Takes a 2D input path and returns a path offset by the specified amount.  As with the built-in
 //   offset() module, you can use `r` to specify rounded offset and `delta` to specify offset with
 //   corners.  If you used `delta` you can set `chamfer` to true to get chamfers.
-//   Positive offsets shift the path to the left (relative to the direction of the path).
+//   Positive offsets shift the path to the left (relative to the direction of the path).  Note
+//   that the path must not include any 180 degree turns, where the path reverses direction.  
 //   .
 //   When offsets shrink the path, segments cross and become invalid.  By default `offset()` checks
 //   for this situation.  To test validity the code checks that segments have distance larger than (r
@@ -831,7 +832,7 @@ function offset(
             (len(sharpcorners)==2 && !closed) ||
             all_defined(closed? sharpcorners : select(sharpcorners, 1,-2))
     )
-    assert(parallelcheck, "Path contains sequential parallel segments (either 180 deg turn or 0 deg turn")
+    assert(parallelcheck, "Path contains a segment that reverses direction (180 deg turn)")
     let(
         // This is a boolean array that indicates whether a corner is an outside or inside corner
         // For outside corners, the newcorner is an extension (angle 0), for inside corners, it turns backward
diff --git a/rounding.scad b/rounding.scad
index 425db47..3fca7d5 100644
--- a/rounding.scad
+++ b/rounding.scad
@@ -1954,7 +1954,7 @@ function rounded_prism(bottom, top, joint_bot=0, joint_top=0, joint_sides=0, k_b
     assert(debug || bot_simple,
           "Roundovers interfere with each other on bottom face: either input is self intersecting or top joint length is too large")
     assert(debug || (verify_vert==[] && verify_horiz==[]), "Curvature continuity failed")
-    let(
+    let( 
         vnf = vnf_merge([ each subindex(top_samples,0),
                           each subindex(bot_samples,0),
                           for(pts=edge_points) vnf_vertex_array(pts),
diff --git a/vnf.scad b/vnf.scad
index 1534f5c..24fc232 100644
--- a/vnf.scad
+++ b/vnf.scad
@@ -587,7 +587,9 @@ module vnf_wireframe(vnf, width=1)
                     sort([face[i], select(face,i+1)])
                  ]);
   for (e=edges) extrude_from_to(vertex[e[0]],vertex[e[1]]) circle(d=width);
-  move_copies(vertex) sphere(d=width);
+  // Identify vertices actually used and draw them
+  vertused = search(count(len(vertex)), flatten(edges), 1);
+  for(i=idx(vertex)) if(vertused[i]!=[]) move(vertex[i]) sphere(d=width); 
 }
 
 
@@ -687,6 +689,8 @@ function vnf_centroid(vnf) =
 //   cut_knot = vnf_halfspace([1,0,0,0], knot);
 //   vnf_polyhedron(cut_knot);
 function vnf_halfspace(plane, vnf, closed=true) =
+    assert(_valid_plane(plane), "Invalid plane")
+    assert(is_vnf(vnf), "Invalid vnf")
     let(
          inside = [for(x=vnf[0]) plane*[each x,-1] >= 0 ? 1 : 0],
          vertexmap = [0,each cumsum(inside)],