'Duplex Pyramids' below is the logo of the Natural Systems Institute.  The top inverted pyramid represents layers of  external structures and systems and the bottom pyramid represents layers of internal structures and systems.  The extension of the pyramid to the left represents degrees of distance into the past, while extension to the right represents degrees of projection into the future.  The underlying theoretical assumption is that effective, enduring change in humans and human social systems comes only when these multidimensional relationships of the external, internal, past and future perspectives are all addressed as change efforts are attempted.