proposition: 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)).
proof: Proof. exact (rmatch _ _ _). Qed.
imports: Bool List BinPos Pnat Setoid SetoidList PeanoNat