| validrefs(str, r ' + refs0, (st -- r0)[r -- _type] .type, st -- r0) ⊦ cyclic(str, r, st), ¬ r ∈ refs0 ∧ ¬ dups(refs0) |
⊦ cyclic(str, r, st) ↔ (∃ refs. dups(refs) ∧ refs .first = r ∧ validrefs(str, refs, st[r -- _type] .type, st))
validrefs(str, r ' + refs0, (st -- r0)[r -- _type] .type, st -- r0) ⊦ ∃ refs. dups(refs) ∧ refs .first = r ∧ validrefs(str, refs, st[r -- _type] .type, st), ¬ r ∈ refs0 ∧ ¬ dups(refs0)
[[CONCRETESIMPRULES : ()], [EXTRATERMS : (st, r, str)]]