Ltac spec H := match type of H with ?A -> _ =>
let H' := fresh in (assert (H' : A); [ | specialize (H H'); clear H']) end.

Lemma treeify'_g_is_redblack:
forall n l,
S (length l) >= nat_of_P n ->
is_redblack (fst (treeify_g n l)) Red (plog2 n).