⊦ r -- sk ∈ st → r ∈ st
⊦ (st -- r0)[r0 -- sk] = ∅[r0 -- sk], r0 ∈ st, r0 -- sk ∈ st
[[CONCRETESIMPRULES : ([CSIMPSEQ : ⊦ ¬ rk ∈ st → st[rk] = ∅[rk]])]]