| r -- sk ∈ st ∪ st0, r ∈ st ∪ st0 ⊦ ∃ sk. r -- sk ∈ st, ∃ sk. r -- sk ∈ st0 |
⊦ rk ∈ st ∪ st0 ↔ rk ∈ st ∨ rk ∈ st0
r -- sk ∈ st ∨ r -- sk ∈ st0, r ∈ st ∪ st0 ⊦ ∃ sk. r -- sk ∈ st, ∃ sk. r -- sk ∈ st0
[[CONCRETESIMPRULES : ()], [EXTRATERMS : (st0, st, r -- sk)]]