Hi, I don't really understand why the last line doesn't work (example should run with any dataset that has the "index" generic variable): <hansl> list checkl = index series st = index^2 checkl += st checkl += log(index) checkl += index^2 # fails </hansl> The on-the-fly transformation doesn't seem to be a problem per se, or else log(index) would also fail. Could it be that the "^" operation is mistaken by gretl to be the special interaction thingy? (Which should only kick in if the right-hand argument is a series or list, not a number like the 2 here.) This is with the June 29th snapshot on Windows. Thanks, sven