I was work... continuing to work on the level splitting in crystals and wanted to know now how rare earth atoms actually looked, and so I used the Fermi Atom. That is Fermi had applied his... his statistics to obtain the simple picture of an atom which gave the charge distribution of the electrons, and so I used that for the typical rare earth and calculated the wave functions of electrons in that potential. And I was very proud when Fermi then told me 'You should put that in to my Thesaurus piarum; the treasury of wave functions', and I don't know whether that was preserved, but anyway there it was. I never did anything. And then we did the... this joint paper about various approaches to relativistic collision theory and I wrote a paper on... on the stopping of electrons... of relativistic electrons, which Fermi then later on modified. Then taking into account that in a solid, or in any condensed material there is a dielectric constant, and you have to take that into account, and that reduces the stopping power somewhat.