code: @Pure
  	public boolean contains(int number) {
  		if (isEmpty())
  			return false;
  		if(step == -1)
  			return number <= first && number >= last;
  		else
  			return number >= first && number <= last;
  	}
docs: Checks whether this contains the given number, i.e. whether the iterator will yield the number. This is different
  from interval containment: <code>0..2.by(2)</code> will <em>not</em> contain 1.
  
  @param number
  the number to be checked for containment.
  @return whether this sequence contains the given number or not.