anchor.diff:                                          let ithSymbolFollowSet' =
                                               /// The FOLLOW set for the current nonterminal.
                                               let nontermFollowSet = Map.find nontermId followSets
  -
  +                                            // Merge it with the FOLLOW set for the i-th symbol.
                                               Set.union ithSymbolFollowSet nontermFollowSet
   
                                           // Set the 'updated' flag iff the i-th symbol's FOLLOW set
  
positive.code:                             | Symbol.Terminal _ -> ()
                              | Symbol.Nonterminal ithSymbolNontermId ->
                                  for j = i + 1 to k do
                                      if i = k ||
                                          // OPTIMIZE : Array slices are slow -- find another way to implement this.
                                          production.[i + 1 .. k]
                                          |> Array.forall (function
                                              | Symbol.Terminal _ ->
                                                  false
                                              | Symbol.Nonterminal nontermId ->
                                                  Map.find nontermId nullable) then
  
                                          /// The FOLLOW set for the i-th symbol in the production.
                                          let ithSymbolFollowSet = Map.find ithSymbolNontermId followSets
  
  
negative.code:                         let mutable updated = updated
  
                          for i = 0 to Array.length production - 1 do
                              if i = 0 || allNullableInSlice (production, 0, i - 1, nullable) then
                                  /// The FIRST set for the current nonterminal.
                                  let nontermFirstSet = Map.find nontermId firstSets
                                  
                                  /// The updated FIRST set for the current nonterminal.
                                  let nontermFirstSet' =
                                      /// The FIRST set for the i-th symbol in the production.
                                      let symbolFirstSet =
                                          match production.[i] with
                                          | Symbol.Terminal token ->
                                              Set.singleton token
                                          | Symbol.Nonterminal nontermId ->
                                              Map.find nontermId firstSets
                                      
                                      Set.union nontermFirstSet symbolFirstSet
  
                                  // Set the 'updated' flag iff the nonterminal's FIRST set
                                  // was actually changed.
  