| junkref(str, r0, st), ∃ refs. refs ≠ [] ∧ refs .first = r ∧ refs .last = r0 ∧ validrefs(str, refs, st[r -- _type] .type, st) ⊦ junkref(str, r, st) |
junkref(str, refs .last, st), validrefs(str, refs, st[refs .first -- _type] .type, st) ⊦ refs = [], junkref(str, refs .first, st)
[[CONCRETESIMPRULES : ()]]