module type S2 = sig .. end
sig
end
include Traversable.Basic2
val sequence : ('u, 'a) f t -> ('u, 'a t) f
('u, 'a) f t -> ('u, 'a t) f
val sequence_ : ('u, 'a) f t -> ('u, unit) f
('u, 'a) f t -> ('u, unit) f