my name is Tadej Rojac and I'm writing from the Institute Jozef Stefan in Ljubljana, Slovenia. I work in the Department of electronic ceramics. Actually, I'm working on a EXAFS spectra with Artemis. What I am trying to do is mainly to describe an EXAFS spectrum with a model concerning the structure of Nb2O5. I'm working togheter with prof. Iztok Arcon, who is a specialist in the field. My main problem is that I have to do some suppositions. In fact Nb2O5 structure is quite complicated. It is composed of seven different Nb positions which I took into account using 7 feffs in Artemis. I don't know the exact occupancies of the seven positions. In order to make the search easier I did at first a supposition that all the occupancies must be positive, which is realistic. I set this with the command "abs" in each feff file. Secondly, I need to supose that the sum of all occupancies is 1. In that way the search for the result is much easier, otherwise I get the sum greater than one, which, for sure, is not the case. My question is how can I do that? For example, if the occupancies are O1, O2, O3, O4, O5, O6 and O7 and I define them with a starting value (let use say the same, so 1/7) than I can do O = O1+O2+O3+O4+O5+O6+O7. Finally I need to do O =1, but here Artemis doesn't want to define the same parameter (O in this case) twice. So, how can I insert the conditions, that the sum of all the occupancies is 1, into Artemis? I hope you can help me.