Hint Resolve tree_rep_nullval: saturate_local.

Lemma body_turn_left: semax_body Vprog Gprog f_turn_left turn_left_spec.
Definition pushdown_left_inv (b_res: val) (t_res: tree val): environ -> mpred :=
EX b: val, EX ta: tree val, EX x: Z, EX v: val, EX tb: tree val,
PROP  ()
LOCAL (temp _t b)
SEP   (treebox_rep (T ta x v tb) b;
(treebox_rep (pushdown_left ta tb) b -* treebox_rep t_res b_res)).