⊦ exactarray(r, ty, st) → r ≠ jvmref ∧ r ∈ st
exactarray(r, ty, st), st[r -- _length] .intval < 0, r ∈ st ⊦ r = jvmref
[[CONCRETESIMPRULES : ([CSIMPFORWARD : ⊦ j < i ∧ i ≤ 0 → j < 0])]]