public class Visa {
	private Citizen owner;
	private int validFor;
	
	public Visa(Citizen issuedOwner, int validForPeriod) {
		owner = issuedOwner;
		validFor = validForPeriod;
	}
	
	public boolean validate(Citizen possessor) {
		return possessor.equals(owner);
	}
}

public abstract class Person {
	protected boolean gender;
	
	public final static boolean MALE = true;
	public final static boolean FEMALE = false;
	
	private String birthname;
	public String nickname;
	
	private Person() {}
	
	public Person(boolean gender, String name) {
		this.gender = gender;
		birthname = nickname = name;
	}
	
	protected boolean getGender()	{	return gender;		}
	public String getBirthname() 	{	return birthname;	}
	public abstract String say(String statement);
}