| st ⊆ st1, validrefkeynotnull(str, rk, ty, st) ⊦ validrefkeynotnull(str, rk, ty, st1) |
⊦ validrefkeynotnull(str, rk, ty, st) ↔ rk ∈ st ∧ validrefvalnotnull(str, st[rk], ty, st)
st ⊆ st1, rk ∈ st ∧ validrefvalnotnull(str, st[rk], ty, st) ⊦ validrefkeynotnull(str, rk, ty, st1)
[[CONCRETESIMPRULES : ()], [EXTRATERMS : (st, ty, rk, str)]]