In more complex cases[citation needed] (e.g. Civilization) every technology above the starting level has more than one prerequisite and one has to research most of the lower-level technologies in order to research any of the top-level technologies. And there are many possibilities between these two variants, for example in Space Empires researching to a specified level in one field may enable the player both to research to a higher level in that field and to start research in a new field which was previously not available.[1]