Am 06.10.2017 um 15:01 schrieb Allin Cottrell: Yes of course. But suppose you want the lags indicated by seq(3, hilag), so you just want to skip the first two lags, and the user may choose hilag. In general hilag=3 would be perfectly admissible, but would lead to this problem. A workaround for this particular example might be "lags(hilag, y) - lags(2, y)"; although I could construct more complicated examples where the problem would come back. One solution might be to introduce a further optional arg to lags() to clarify the intent, but since that fucntion already has an optional arg (and as all args in hansl are positional), this would probably get cumbersome. -sven