Somehow I didn't see your reply till now. It turns out this problem of computed cell references is a nontrivial one. (Excel can do it, but slowly and I suspect

Somehow I didn't see your reply till now. It turns out this problem of computed cell references is a nontrivial one. (Excel can do it, but slowly and I suspect not with full generality.) The trouble is that you need the reference graph to compute the spreadsheet, but now computing the spreadsheet can modify the reference graph, so you have to maintain the graph dynamically as you calculate. I'd be interested in discussing this further if you are, but email would be better than here. (My address is in my profile.)