let matches = seq { for line in (File.ReadLines(@"L:/foo.txt")) -> r.Matches(line) }
let extract (matches : seq<MatchCollection>) =
    seq {
        for ms in matches do
            for m in ms -> m.Value.TrimEnd([|'<'|])
     }
     |> Seq.map (fun x -> x, "") |> dict |> Seq.map (fun x -> x.Key)