Definition bitseq := seq bool.

(* Specifications: *)
Lemma incr_nth_inj v : injective (incr_nth v).
Lemma incr_nthC v i j : incr_nth (incr_nth v i) j = incr_nth (incr_nth v j) i.
Lemma perm_eqP s1 s2 : reflect (count^~ s1 =1 count^~ s2) (perm_eq s1 s2).
Lemma perm_eq_refl s : perm_eq s s.
Lemma perm_eq_sym : symmetric perm_eq.
Lemma perm_eq_trans : transitive perm_eq.