@Override
  public boolean equals(Object obj)
  { if(obj instanceof Triple)
    { Triple that=(Triple)obj;
      /*if(this.r==null||this.s==null||this.t==null||that.r==null||that.s==null||that.t==null)
      { return false;}
      else*/
      { return this.r.equals(that.r)&&this.s.equals(that.s)&&this.t.equals(that.t);}
    }
    else 
    { throw new RuntimeException(obj+" should be of Triple type?");
    }
  }