Ed Greshko wrote: > I think this illustrates what I think you're seeing..... > https://drive.google.com/file/d/0B2H9v1dYNcvpX2FuQ3F5OEhjeTA/edit?usp=sharing Indeed. Do you consider this display self-explanatory? -- Timothy Murphy e-mail: gayleard /at/ eircom.net School of Mathematics, Trinity College, Dublin 2, Ireland