After this morning's discussion I implemented what I've had in mind to make the implementation of my library standard generic programming. It is just a demonstration of the GP interfaces I have in mind, and is pretty simple. I define a point, interval, point_3d and rectangle concepts and use them with each other. For example the point_3d is also a model for point_2d, and I use it that way, and the rectangle interface is implemented in terms of the interval. The coordinate type is templated everywhere and I use that fact to demonstrate the compatibility that enables between geometry objects with different coordinate data types. Near the end I show how a made up layout object data type, that has the four coordinates of a rectangle as part of its member data, can be made to model the rectangle concept by providing a specialization of rectangle_traits for it and then I use it with another rectangle type with different coordinate type. Please feel free to critique the code. I want to make sure I've got everything right before I rewrite the library. Thanks, Luke