anchor.diff:                      "The file to load (omit, or supply -, for standard input).")>]
             input : string option }
   
  -    let _emptyOpts = {
  +    let _emptyOpts : Options = {
           raw             = false;
           backendOpts     = None;
           stage           = None;
  
positive.code:     |> Seq.map (fun x -> x.Trim())
  
  
  /// Converts a list to an option that is Some iff it has exactly one item.
  let onlyOne s =
      s
      |> List.ofSeq
      |> function
  
negative.code:  * Map data structure
   *)
  
  /// Tries to find duplicate entries in a sequence.
  /// Returns a sequence of the duplicates found.
  let findDuplicates (s : 'A seq) : 'A seq =
      s
      |> Seq.groupBy id
      |> Seq.choose
             // dupes now contains all of the appearances of x.
  