| ¬ ¬ is_valid_ref(r0, st -- r), has_reffield(r0, st -- r) ⊦ has_reffield(r0, st), r0 = r |
⊦ r ≠ r0 → (is_valid_ref(r, st -- r0) ↔ is_valid_ref(r, st))
has_reffield(r0, st -- r), is_valid_ref(r0, st) ⊦ r0 = r, has_reffield(r0, st)
[[CONCRETESIMPRULES : ()]]