I have difficulty understanding this statement in DL:
∃R.∃S.C(a)
What does this proposition exactly mean? Thanks in advance!
This means that the individual named a belongs to the concept ∃R.∃S.C. The concept ∃R.∃S.C represents the class of things that have a relation R with something that has a relation S with something that is in the class denoted by C. For instance, if R is the relation married to, S is the relation works for and C is the class of Public organisations, then ∃R.∃S.C represents all the entities that are married to something (or someone) that works for a public organisation. Then ∃R.∃S.C(a) means that the individual named a is such an entity.