| validrefkeynotnull(str, rk, ty, st1) ⊦ st1[rk] = (st ∪ st1)[rk] |
⊦ validrefkeynotnull(str, rk, ty, st) ↔ rk ∈ st ∧ validrefvalnotnull(str, st[rk], ty, st)
[[CONCRETESIMPRULES : ([CSIMPSEQ : ⊦ rk ∈ st0 → (st ∪ st0)[rk] = st0[rk]])], [EXTRATERMS : (st1, ty, rk, str)]]