| st ⊆ st0 ⊦ validrefs(str, r ' + refs, ty, st0) ↔ validrefs(str, r ' + refs, ty, st), junkref(str, r, st) |
⊦ validref(str, r, st[r -- _type] .type, st) ∧ st ⊆ st0 → (validrefs(str, r ' + refs, ty, st0) ↔ validrefs(str, r ' + refs, ty, st))
¬ (validref(str, r, st[r -- _type] .type, st) ∧ st ⊆ st0), st ⊆ st0 ⊦ validrefs(str, r ' + refs, ty, st0) ↔ validrefs(str, r ' + refs, ty, st), junkref(str, r, st)
[[CONCRETESIMPRULES : ()], [EXTRATERMS : (str, r, st, st0, refs, ty)]]