#[global]
Instance rbalS_ok l x r :
forall `(Ok l, Ok r, lt_tree x l, gt_tree x r), Ok (rbalS l x r).
Global Hint Rewrite lbalS_spec rbalS_spec : rb.
(** ** Append for deletion *)
Ltac append_tac l r :=
induction l as [| lc ll _ lx lr IHlr];
[intro r; simpl
|induction r as [| rc rl IHrl rx rr _];
[simpl
|destruct lc, rc;
[specialize (IHlr rl); clear IHrl
|simpl;
assert (Hr:notred (Bk rl rx rr)) by (simpl; trivial);
set (r:=Bk rl rx rr) in *; clearbody r; clear IHrl rl rx rr;
specialize (IHlr r)
|change (append _ _) with (Rd (append (Bk ll lx lr) rl) rx rr);
assert (Hl:notred (Bk ll lx lr)) by (simpl; trivial);
set (l:=Bk ll lx lr) in *; clearbody l; clear IHlr ll lx lr
|specialize (IHlr rl); clear IHrl]]].
Fact append_rr_match ll lx lr rl rx rr :
rspec
(fun a x b => Rd (Rd ll lx a) x (Rd b rx rr))
(fun t => Rd ll lx (Rd t rx rr))
(append lr rl)
(append (Rd ll lx lr) (Rd rl rx rr)).
Fact append_bb_match ll lx lr rl rx rr :
rspec
(fun a x b => Rd (Bk ll lx a) x (Bk b rx rr))
(fun t => lbalS ll lx (Bk t rx rr))
(append lr rl)
(append (Bk ll lx lr) (Bk rl rx rr)).

Lemma append_spec l r x :
InT x (append l r) <-> InT x l \/ InT x r.