Hint Resolve tree_rep_nullval: saturate_local.

Lemma body_pushdown_left: semax_body Vprog Gprog f_pushdown_left pushdown_left_spec.
Definition delete_inv (b0: val) (t0: tree val) (x: Z): environ -> mpred :=
EX b: val, EX t: tree val,
PROP()
LOCAL(temp _t b; temp _x (Vint (Int.repr x)))
SEP(treebox_rep t b;  (treebox_rep (delete x t) b -* treebox_rep (delete x t0) b0)).