| C[t3] => t2, context(C), t3 =>top t0 ⊦ C[t0] = t2 |
⊦ t => t' ↔ (∃ C, t0, t1. context(C) ∧ t = C[t0] ∧ t0 =>top t1 ∧ t' = C[t1])
∃ C0, t0, t1. context(C0) ∧ C[t3] = C0[t0] ∧ t0 =>top t1 ∧ t2 = C0[t1], context(C), t3 =>top t0 ⊦ C[t0] = t2
[[CONCRETESIMPRULES : ()], [EXTRATERMS : (t2, C[t3])]]