Pecoflyer, thanks for pointing me in this direction. I took this long to figure out how to make it work, not because your directions were wrong or even unclear but because I had to keep fooling with them them, many different ways ("why does it work when I do this but not when I do this? They seem equivalent"). The point, as you may already understand, was not for me to make it work, but to understand how it works.

I'm still having trouble with it, because sometimes I can make array arithmetic work without <Ctrl-Shift-Enter> and sometimes not. In the latter cases, the formula bar claims that it's working correctly (that the MATCH function is returning 2, for example), yet what's actually displayed in the worksheet is #N/A—unless I use <Ctrl-Shift-Enter>. I don't suppose you know why, by any chance?