sig   val copy :     string ->     string ->     (unit,      [> `Synchronize of           string * string *           [> `Database of Ketrew.Persistent_data.Error.database            | `IO of                [> `Read_file_exn of string * exn                 | `Write_file_exn of string * exn ]            | `System of                [> `File_info of string                 | `List_directory of string                 | `Make_directory of string ] *                [> `Exn of exn | `Wrong_access_rights of int ]            | `Target of [> `Deserilization of string ]            | `Unknown_uri_scheme of string * string option            | `Weird_file of string ] ])     Unix_io.Deferred_result.t   module Error :     sig       val to_string :         string * string *         [< `Database of Ketrew.Persistent_data.Error.database          | `IO of              [< `Exn of exn               | `File_exists of string               | `Read_file_exn of string * exn               | `Write_file_exn of string * exn               | `Wrong_path of string ]          | `System of              [< `Copy of string               | `File_info of string               | `File_tree of string               | `List_directory of string               | `Make_directory of string               | `Make_symlink of string * string               | `Move of string               | `Remove of string ] *              [< `Already_exists               | `Exn of exn               | `File_exists of string               | `File_not_found of string               | `IO of                   [< `Exn of exn                    | `File_exists of string                    | `Read_file_exn of string * exn                    | `Write_file_exn of string * exn                    | `Wrong_path of string ]               | `Not_a_directory of string               | `Wrong_access_rights of int               | `Wrong_file_kind of string * Pvem_lwt_unix.System.file_info               | `Wrong_path of string ]          | `Target of [< `Deserilization of string ]          | `Unknown_uri_scheme of string * string option          | `Weird_file of string ] ->         string     end end