anchor.diff:          // Return the computed set of indices.
           accepting
   
  -    /// The indices of the element expressions (if any)
  -    /// that accept the empty string (epsilon).
  -    let acceptingElementsTagged< [<Measure>] 'Tag > (regVec : RegularVector) =
  -        /// The indices of the expressions accepting the empty string.
  -        let mutable accepting = Set.empty
  -
  -        let len = Array.length regVec
  -        for i = 0 to len - 1 do
  -            if Regex.IsNullable regVec.[i] then
  -                accepting <- Set.add (Int32WithMeasure<'Tag> i) accepting
  -
  -        // Return the computed set of indices.
  -        accepting
  -
       /// Determines if a regular vector is an empty vector. Note that an
       /// empty regular vector is *not* the same thing as an empty array.
       let inline isEmpty (regVec : RegularVector) =
  
positive.code:                 |> cont
          | Star r as ``r*`` ->
              Regex.DerivativeImpl wrtSymbol r <| fun r' ->
                  Concat (r', ``r*``)
                  |> cont
          | Concat (r, s) ->
              let ``nu(r)`` = if Regex.IsNullable r then Epsilon else Empty
  
negative.code:         | Epsilon ->
              cont Empty
          | Any ->
              cont Epsilon
          | Character c ->
              if c = wrtSymbol then Epsilon else Empty
  