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))))))