Hi Bill: I wanted to run this question by you because its sort of skewing my understanding of the Set class heirarchy: Why is there a field "ManifoldDimension" in a SimpleSet? To ask that in a more roundabout way: The definition of the Set class more or less corresponds to my idea of a set. When I get to SimpleSet, though, and you add the idea of a manifold dimension, it seems you are defining a manifold. If I use the simple definition of manifold as "a subset of Rn, along with an invertable and differentiable function phi:Rm -> Rn", then are you adding the function phi to the class SimpleSet? When I examine the subclasses of SimpleSet, it seems that GriddedSet and its subclasses define phi in the gridToValue() method. DoubleSet, FloatSet, and List1DSet all seem to just be plain sets.