diff --git a/openscad_py.py b/openscad_py.py
index e3b3513..db69a61 100644
--- a/openscad_py.py
+++ b/openscad_py.py
@@ -1,5 +1,5 @@
 
-from typing import Union
+from typing import Union as TUnion
 import math
 import numpy as np
 
@@ -14,7 +14,7 @@ class Point:
         self.c = np.array(coords, dtype=NP_TYPE)
         
     @classmethod
-    def c(cls, coords: Union[list, 'Point']) -> 'Point':
+    def c(cls, coords: TUnion[list, 'Point']) -> 'Point':
         """Ensure coords is an instance of Point"""
         if isinstance(coords, Point):
             return coords
@@ -22,7 +22,7 @@ class Point:
 
     def render(self) -> str:
         """Render the point into a SCAD script"""
-        return ",".join([str(c) for c in self.c])
+        return "[" + (",".join([str(c) for c in self.c])) + "]"
 
     def scale(self, x: float) -> 'Point':
         """Scale the current vector/point by a scalar"""
@@ -136,36 +136,58 @@ class Object:
     def _center(self) -> str:
         return ('true' if self.center else 'false')
     
-    def add(self, obj):
+    def _add(self, obj):
+        """Add an object, forming a collection"""
         return Collection([self, obj])
     
     def render(self) -> str:
         raise Exception("abstract method")
     
-    def translate(self, v: Union[list, Point]):
+    def translate(self, v: TUnion[list, Point]) -> 'Object':
         """Apply a translation"""
         return Translate(v=v, child=self)
 
-    def move(self, v: Union[list, Point]):
+    def move(self, v: TUnion[list, Point]) -> 'Object':
         """Apply a translation"""
         return Translate(v=v, child=self)
 
-    def rotate(self, a, v: Union[list, Point]):
+    def rotate(self, a, v: TUnion[list, Point]) -> 'Object':
         """Apply a rotation"""
         return Rotate(a=a, v=v, child=self)
 
+    def scale(self, v: TUnion[list, Point, float]) -> 'Object':
+        """Apply scaling. Accepts a single float for uniform scaling"""
+        return Scale(v=v, child=self)
+
+    def color(self, r, g, b, a=1.) -> 'Object':
+        """Apply a color"""
+        return Color(r=r, g=g, b=b, a=a, child=self)
+
+    def extrude(self, height, convexity = 10, center: bool = False) -> 'Object':
+        """Apply a linear extrusion"""
+        return LinearExtrude(height=height, child=self, convexity=convexity, center=center)
+
+    def diff(self, tool: TUnion[list, 'Object']) -> 'Object':
+        """Remove from the object using a difference operator"""
+        return Difference(subject=self, tool=tool)
+
+    def union(self, objects: TUnion[list, 'Object']) -> 'Object':
+        return Union(child=Collection.c(objects)._add(self))
+
 
 class Cube(Object):
+    """A 3D primitive, cube"""
     
-    def __init__(self, size: Union[list, Point], center: bool = False):
+    def __init__(self, size: TUnion[list, Point], center: bool = False):
         self.size = Point.c(size)
         self.center = center
         
     def render(self):
-        return f"cube(size=[{self.size.render()}], center={self._center()});"
+        return f"cube(size={self.size.render()}, center={self._center()});"
 
 
 class Sphere(Object):
+    """A 3D primitive, sphere"""
     
     def __init__(self, r):
         self.r = r
@@ -176,6 +198,7 @@ class Sphere(Object):
 
 
 class Cylinder(Object):
+    """A 3D primitive, cylinder"""
     
     def __init__(self, h, r=None, r1=None, r2=None, center: bool = False):
         self.height = h
@@ -188,7 +211,7 @@ class Cylinder(Object):
         return f"cylinder(h={self.height}, r1={self.r1}, r2={self.r2}, center={self._center()});"
     
     @classmethod
-    def from_ends(cls, radius: float, p1: Union[list, Point], p2: Union[list, Point]) -> Object:
+    def from_ends(cls, radius: float, p1: TUnion[list, Point], p2: TUnion[list, Point]) -> Object:
         """Construct a cylinder between two points"""
         p1 = Point.c(p1)
         p2 = Point.c(p2)
@@ -205,9 +228,42 @@ class Cylinder(Object):
             rangle = 0
             r = z
         return cls(h=length, r=radius, center=False).rotate(a=rangle, v=r).move(p1)
-        
 
 
+class Circle(Object):
+    """A 2D primitive, circle"""
+
+    def __init__(self, r, fn=None):
+        self.r = r
+        self.fn = fn
+        # $fa, $fs, $fn
+
+    @classmethod
+    def triangle(cls, r):
+        """Create a regular triangle"""
+        return cls(r=r, fn=3)
+
+    @classmethod
+    def regular_polygon(cls, r, sides: int):
+        """Create a regular polygon"""
+        return cls(r=r, fn=sides)
+
+    def render(self) -> str:
+        fnstr = '' if self.fn is None else f", $fn={self.fn}"
+        return f"circle(r={self.r}{fnstr});"
+
+
+class Polygon(Object):
+    """A 2D primitive, polygon"""
+
+    def __init__(self, points, paths=None, convexity=1):
+        assert paths is None  # not implemented yet
+        self.points = [Point.c(p) for p in points]
+        self.convexity = convexity
+
+    def render(self) -> str:
+        return f"polygon(points=[{','.join([p.render() for p in self.points])}], convexity={self.convexity});"
+
 # TODO polyhedron(points=[[],], faces[[p,],], convexity=)
 # TODO https://docs.python.org/3/reference/datamodel.html#emulating-numeric-types
 
@@ -216,35 +272,110 @@ class Collection(Object):
     
     def __init__(self, coll: list):
         self.collection = coll
+
+    @classmethod
+    def c(cls, coll: TUnion[list, Object]) -> Object:
+        """Cast lists to collections"""
+        if isinstance(coll, Object):
+            return coll
+        return cls(coll)
     
-    def add(self, obj):
-        self.collection.append(obj)
-        
-    def render(self):
+    def _add(self, obj):
+        return self.__class__(self.collection + [obj])
+
+    def render(self) -> str:
         return "\n".join([o.render() for o in self.collection])
 
 
 class Translate(Object):
     """Represents a translation transformation applied to an object"""
     
-    def __init__(self, v: Union[list, Point], child: Object):
+    def __init__(self, v: TUnion[list, Point], child: Object):
         self.v = Point.c(v)
         self.child = child
         
-    def render(self):
-        return f"translate(v=[{self.v.render()}]){{\n{self.child.render()}\n}}"
+    def render(self) -> str:
+        return f"translate(v={self.v.render()}){{\n{self.child.render()}\n}}"
     
     
 class Rotate(Object):
     """Represents a rotation transformation applied to an object"""
 
-    def __init__(self, a, v: Union[list, Point], child: Object):
+    def __init__(self, a, v: TUnion[list, Point], child: Object):
         self.a = a
         self.v = Point.c(v)
         self.child = child
         
-    def render(self):
-        return f"rotate(a={self.a}, v=[{self.v.render()}]){{\n{self.child.render()}\n}}"
-    
-    
-    
+    def render(self) -> str:
+        return f"rotate(a={self.a}, v={self.v.render()}){{\n{self.child.render()}\n}}"
+
+
+class Scale(Object):
+
+    def __init__(self, v: TUnion[list, Point, float], child: Object):
+        if isinstance(v, float):
+            v = [v, v, v]
+        self.v = Point.c(v)
+        self.child = child
+
+    def render(self) -> str:
+        return f"scale(v={self.v.render()}){{\n{self.child.render()}\n}}"
+
+
+class Color(Object):
+
+    def __init__(self, child: Object, r, g, b, a=1.):
+        self.color = [r, g, b, a]
+        self.child = child
+
+    def render(self) -> str:
+        return f"color(c=[{','.join([str(c) for c in self.color])}]){{ {self.child.render()} }}"
+
+
+class LinearExtrude(Object):
+    """Represents a linear extrusion applied to an object"""
+
+    def __init__(self, height, child: Object, convexity = 10, center: bool = False):
+        self.height = height
+        self.child = child
+        self.convexity = convexity
+        self.center = center
+        # twist, slices, scale (float/vector), $fn
+
+    def render(self) -> str:
+        return f"linear_extrude(height={self.height}, center={self._center()}, convexity={self.convexity}){{\n{self.child.render()}\n}}"
+
+
+class Union(Object):
+    """Represents a union applied to an object (usually a collection of objects)"""
+
+    def __init__(self, child: TUnion[Object, list]):
+        self.child = Collection.c(child)
+
+    def render(self) -> str:
+        return f"union(){{ {self.child.render()} }}"
+
+    def union(self, objects: TUnion[list, Object]) -> Object:
+        return self.__class__(self.child._add(objects))
+
+
+class Intersection(Object):
+    """Represents an intersection applied to an object (usually a collection of objects)"""
+
+    def __init__(self, child: TUnion[Object, list]):
+        self.child = Collection.c(child)
+
+    def render(self) -> str:
+        return f"intersection(){{ {self.child.render()} }}"
+
+
+class Difference(Object):
+    """Represents a difference"""
+
+    def __init__(self, subject: Object, tool: TUnion[list, Object]):
+        self.subject = subject
+        self.tool = Collection.c(tool)  # what to remove
+
+    def render(self) -> str:
+        return f"difference(){{ {self.subject.render()}\n{self.tool.render()} }}"
+