It would be extremely useful to have a longer explanation of the prepositions (and the genitive) in the introductory/explanatory sections. I have not yet come across an explanation for the formation of στο etc. Maybe it is in the Accusative lesson, which I haven't started yet. Also why don't you add a column in the list of prepositions or an explanation about which prepositions are followed by the genitive and which by the accusative. In any case, thanks for the course. It is done amazingly well!