j < i, 0 ≤ j, 0 < i ⊦ (addarray(r, val, i, st)[r -- j ']) = val
[[CONCRETESIMPRULES : ([CSIMPFORWARD : ⊦ i ≤ j ∧ 0 ≤ i → 0 ≤ j], [CSIMPFORWARD : ⊦ i < j ∧ 0 ≤ i → 0 < j])]]