anchor.diff:  let readInput file =
       File.ReadAllLines file |> Seq.map parseLine |> List.ofSeq
   
  +let availableTasks edges =
  +    let left = edges |> Seq.map fst |> set
  +    let right = edges |> Seq.map snd |> set
  +    Set.difference left right |> Seq.sort
  +
   let solve1 input =
       let rec loop (result:string) (edges:(string * string) list) : string =
           let left = edges |> Seq.map fst |> set
  
positive.code:         | _ -> loop (result + node) newEdges
  
      loop String.Empty input
  
  [<EntryPoint>]
  let main _ =
  
negative.code:         ]
          |> List.map parseLine
      
      //Common.test solve1 [(testInput, "CABDFE")]
      Common.test (fun i -> solve2 time 2 i) [(testInput, 15)]
  
      let result1 = Common.timeResult 1 { return solve1 input }
  
      Console.ReadLine() |> ignore
      0 // return an integer exit code
  