sig   type t =       [ `Defined of Libvirt.Event.Defined.t       | `PMSuspended of Libvirt.Event.PM_suspended.t       | `Resumed of Libvirt.Event.Resumed.t       | `Shutdown       | `Started of Libvirt.Event.Started.t       | `Stopped of Libvirt.Event.Stopped.t       | `Suspended of Libvirt.Event.Suspended.t       | `Undefined of Libvirt.Event.Undefined.t       | `Unknown of int ]   val to_string : Libvirt.Event.Lifecycle.t -> string end