⊦ r ≠ r0 → (update(r0, fis, st)[r -- sk]) = st[r -- sk]
[[CONCRETESIMPRULES : ([CSIMPELIM : ⊦ r = rk .ref ∧ sk = rk .key ↔ rk = r -- sk])], [EXTRATERMS : (rk, r, sk)]]