There are two patterns intertwined. For example, if you had the following pattern:
Fire, Light, Water, Darkness, Air, Earth, ?1, ?2
The odd positions form one pattern: Fire, Water, Air. And the even positions form the other pattern: Light, Darkness, Earth. In this case, both of these patterns would be just advancing one position in the element wheel. So the next element for the odd pattern (?1) would be Light, and the next element for the even pattern (?2) would be Wood.