⊦ r ∈ st ↔ (∃ sk. r -- sk ∈ st)
∃ sk. r -- sk ∈ st, ∀ rk. rk ∈ st → rk .ref ≠ r ⊦ r = jvmref
[[CONCRETESIMPRULES : ()], [EXTRATERMS : (st, r)]]