anchor.diff:              return Negate r'
           | CharacterSet charSet ->
               return
  -                if CharSet.contains wrtSymbol charSet
  -                then Epsilon
  -                else Regex.empty
  +                if CharSet.contains wrtSymbol charSet then
  +                    Epsilon
  +                else
  +                    Regex.empty
           }
   
       /// Computes the derivative of a Regex with respect to a specified symbol.
  
positive.code:     /// Compute the derivative of a regular vector
      /// with respect to the given symbol.
      let inline derivative symbol (regVec : RegularVector) : RegularVector =
          #if PARALLEL_FX
          Array.Parallel.map (Regex.Derivative symbol) regVec
          #else
          Array.map (Regex.Derivative symbol) regVec
          #endif
  
      /// Determines if the regular vector is nullable,
      /// i.e., it accepts the empty string (epsilon).
  
negative.code:     /// The indices of the element expressions (if any)
      /// that accept the empty string (epsilon).
      let acceptingElements (regVec : RegularVector) =
          // Find the indices of the expressions accepting the empty string.
          (Set.empty, regVec)
          ||> Array.foldi (fun i accepting regex ->
              if Regex.IsNullable regex then
                  Set.add i accepting
              else
                  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.
  