let obj = List.nth h (r 'x')
let (a, r', h') = (obj, r, h)
in let u' = (fun e -> unit_dpm (Q e)) a
in u' (r', h')
) else empty_set
let obj = List.nth h (r 'x')
let (a, r', h') = (obj, r, h)
in let u' = (fun e -> unit_dpm (Q e)) a
in u' (r', h')
) else empty_set