| ¬ junkref(str, r, st), ¬ cyclic(str, r, st), is_obj(str, r, st), r ≠ jvmref, ∃ fs, class. fs ' ∈ instfields(class) ∧ fs .type ≤ mkclasstype(class) ∧ st[r -- _type] .type ≤ fs .type ⊦ ∃ refs. validrefs(str, refs, st[r -- _type] .type, st) ∧ refs ≠ [] ∧ ¬ dups(refs) ∧ refs .first = r ∧ refs .last = jvmref |