method tried_emitters ps =
let es = E.Map.fold (fun e _ es -> e::es) ps [] in
match es with
| [] -> ()
| e::es ->
Format.fprintf out "%s@[<hov 2>tried with %a" tab E.pretty e ;
List.iter (fun e -> Format.fprintf out ",@ %a" E.pretty e) es ;
Format.fprintf out ".@]@\n"