Hint Resolve tree_rep_nullval: saturate_local.

Lemma treebox_rep_internal: forall l x v r b p,
Int.min_signed <= Z.of_nat x <= Int.max_signed ->
tc_val (tptr Tvoid) v ->
data_at Tsh (tptr t_struct_tree) p b *
field_at Tsh t_struct_tree [StructField _key] (Vint (Int.repr (Z.of_nat x))) p *
field_at Tsh t_struct_tree [StructField _value] v p *
treebox_rep l (field_address t_struct_tree [StructField _left] p) *
treebox_rep r (field_address t_struct_tree [StructField _right] p) |--
treebox_rep (T l x v r) b.