anchor.diff:      tasknotes.add(note);
     }
     
  -  void addCategory(String cat ) {
  +  void addCategory(TaskCategory cat ) {
       taskcategories.add(cat);
     }
  -  void removeCategory(String cat) {
  +  void removeCategory(TaskCategory cat) {
       taskcategories.remove(cat);
     }
   }
  
positive.code: library task;
  
  import 'dart:convert';
  
  class TaskNote {
    String notebody;
  
negative.code:   List<TaskNote> tasknotes = [];
    DateTime scheduled;
    int timestamp;
    Set<TaskCategory> taskcategories = new Set();
    Task(this.summary, [this.scheduled=null]) {
      this.timestamp = new DateTime.now().millisecondsSinceEpoch;
    }
  