Two entities whatsoever within the same time-span. Here there is also a localization restriction, useful to accomplish a relevance criterion usually implicit in coexistence (specially in biomedicine). This is useful for 'co-occurrence' involving non-temporalized entities.
(=> (Co-Exist ?A ?B) (Exists (?Z) (And (Time-Span ?Z) (Temporally-Contains ?Z ?A) (Temporally-Contains ?Z ?B) (Exists (?W) (And (Region ?W) (Located ?W ?A) (Located ?W ?B))))))