m ≤ # buf, m0 ≤ m, m0 ≤ # buf ⊦ datasize(subarray(buf, 0, m), m0) = datasize(buf, m0)
[Concretesimprules((Csimpnamedforward(nat,,let, ⊦ n ≤ n0 ∧ n0 ≤ n1 → n ≤ n1)))]