abstract class Comparable {
  
  /** Return whether I am less than other? */
  abstract boolean lessThan(Comparable other);

  /** Return whether I am less than or equal to other? */
  boolean lessThanOrEqual (Comparable other){
    return (this.lessThan(other) || this.equals(other));
  }

  /** Return whether I am greater than other? */
  boolean greaterThan (Comparable other){
    return (!this.lessThanOrEqual(other));
  }

  /** Return whether I am greater than or equal to other? */
  boolean greaterThanOrEqual(Comparable other){
    return (!this.lessThan(other));
  }
}