old_contents: 
  export class Date{
      constructor(day, hour, min){
          this.day = day
          this.hour = hour;
          this.min = min;
      }
  }
  
  export class Event{
      constructor(name) {
          this.name = name;
      }
  }
  
  export class EventOption{
      constructor(event, option, instances) {
          this.event = event;
          this.option = option;
          this.instances = instances;
      }
  }
  
  export class EventOptionInstance{
      constructor(day, start, end){
          this.day = day;
          this.start = start;
          this.end = start;
      }
  }
  
new_contents: 
  export class Date{
      constructor(day, hour, min){
          this.day = day;
          this.hour = hour;
          this.min = min;
      }
  
      /*
          if a < b    : return -1
          if a == b   : return 0
          if a > b    : return 1
      */
      static compare(a, b){
          if (a.day<b.day)
              return -1;
          if (a.day>b.day)
              return 1;
          if (a.hour<b.hour)
              return -1;
          if (a.hour>b.hour)
              return 1;
          if (a.min<b.min)
              return -1;
          if (a.min>b.min)
              return 1;
          return 0;
  
      }
  }
  
  export class Event{
      constructor(name) {
          this.name = name;
      }
  }
  
  export class EventOption{
      constructor(event, option, instances) {
          this.event = event;
          this.option = option;
          this.instances = instances;
      }
  }
  
  export class EventOptionInstance{
      constructor(start, end){
          this.start = start;
          this.end = start;
      }
  }
  
subject: Fix last commit