Hi Matthias, thanks for your sample... Am Freitag 05 Oktober 2007 18:11 schrieb Matthias Messmer: > if x == 0 [ > return 1 > ] > else [ "else" is not known, but this way it works: learn poweroftwo x [ if x == 0 return 1 return 2 * poweroftwo x-1 ] clear print poweroftwo 6