let first_revision revs =
(* let order n1 n2 =
match n1, n2 with
[], (_::_) ->
| _, [] -> false
| (id1 :: q1), (id2 :: q2) ->
(id1 < id2) or
((id1 = id2) && (order q1 q2))
in
*)
match List.sort (fun r1 -> fun r2 -> compare r1.rev_number r2.rev_number) revs
with
[] -> None
| h :: _ -> Some h