| refs .last = refs0 .first, validrefs(str, refs0, ty0, st), validrefs(str, refs, ty, st) ⊦ refs = [], refs0 = [], validrefs(str, refs + refs0 .rest, ty, st) |
refs0 = r + refs1, refs .last = r, validrefs(str, refs0, ty0, st), validrefs(str, refs, ty, st) ⊦ refs = [], refs0 = [], validrefs(str, refs + refs1, ty, st)
[[CONCRETESIMPRULES : ([CSIMPELIM : refs ≠ [] ⊦ r = refs .first ∧ refs0 = refs .rest ↔ refs = r + refs0])], [EXTRATERMS : (refs0, r, refs1)]]