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