I'm sparing gretl-users the gory detail ;-) On Sat, 14 Mar 2015, Sven Schreiber wrote: Yes, the statement would be read pretty much as you say. However, "drop" and "first" will not be the names of series in the list created by dummify(Z5), nor in fact by any invocation of dummify(). What if they're the names of scalars? Well, it's possible to cook up a case where something of the sort appears to "work": <hansl> open data4-1 list X = 1 2 3 list X print scalar drop = -4 scalar first = 3 list Y = X --drop-first list Y print </hansl> This actually exposes a little bug. The "+" operator is not recognized for adding a term to a list (simple concatentation is how that's supposed to work), but when it's disguised as "--" it somehow slips through, although it doesn't have the effect of adding series number 4 to list Y. I'll take a look at fixing that. On your broader point -- something that's really an error from the user's point of view may under certain conditions go through as a totally unintended command -- well, I think that's the price to be paid for flexibility. I don't think we want to be saying to users "Did you really mean minus minus?" Allin