| validrefs(str, r ' + refs, ty, st), r0 ∈ refs, validrefs(str, r ' + refs, st[r -- _type] .type, st) ⊦ path∃(str, r, r0, st) |
⊦ path∃(str, r, r0, st) ↔ (∃ refs. refs ≠ [] ∧ refs .first = r ∧ refs .last = r0 ∧ validrefs(str, refs, st[r -- _type] .type, st))
validrefs(str, r ' + refs, ty, st), r0 ∈ refs, validrefs(str, r ' + refs, st[r -- _type] .type, st) ⊦ ∃ refs. refs ≠ [] ∧ refs .first = r ∧ refs .last = r0 ∧ validrefs(str, refs, st[r -- _type] .type, st)
[[CONCRETESIMPRULES : ()], [EXTRATERMS : (st, r0, r, str)]]