anchor.diff:   */
   class BottomTypeImpl extends TypeImpl {
     /**
  -   * The unique instance of this class, with indeterminate nullability.
  -   */
  -  static final BottomTypeImpl instance = instanceIndeterminate;
  -
  -  /**
  -   * The unique instance of this class, nullable.
  -   */
  -  static final BottomTypeImpl instanceNullable =
  -      new BottomTypeImpl._(NullabilitySuffix.question);
  -
  -  /**
  -   * The unique instance of this class, with indeterminate nullability.
  -   */
  -  static final BottomTypeImpl instanceIndeterminate =
  -      new BottomTypeImpl._(NullabilitySuffix.star);
  -
  -  /**
  -   * The unique instance of this class, non-nullable.
  -   */
  -  static final BottomTypeImpl instanceNonNullable =
  -      new BottomTypeImpl._(NullabilitySuffix.none);
  -
  -  @override
  -  final NullabilitySuffix nullabilitySuffix;
  +   * The unique instance of this class.
  +   */
  +  static final BottomTypeImpl instance = new BottomTypeImpl._();
   
     /**
      * Prevent the creation of instances of this class.
      */
  -  BottomTypeImpl._(this.nullabilitySuffix) : super(null, "<bottom>");
  +  BottomTypeImpl._() : super(null, "<bottom>");
   
     @override
     int get hashCode => 0;
   
     @override
     bool get isBottom => true;
  +
  +  @override
  +  NullabilitySuffix get nullabilitySuffix => NullabilitySuffix.none;
   
     @override
     bool operator ==(Object object) => identical(object, this);
  
positive.code:  * `...`.
   */
  class CircularTypeImpl extends DynamicTypeImpl {
    CircularTypeImpl() : super._circular(NullabilitySuffix.star);
  
    @override
    bool operator ==(Object object) => object is CircularTypeImpl;
  
negative.code:  */
  class DynamicTypeImpl extends TypeImpl {
    /**
     * The unique instance of this class.
     */
    static final DynamicTypeImpl instance = new DynamicTypeImpl._();
  
    /**
     * Prevent the creation of instances of this class.
     */
    DynamicTypeImpl._()
        : super(new DynamicElementImpl(), Keyword.DYNAMIC.lexeme) {
      (element as DynamicElementImpl).type = this;
    }
  