public class RussianDoll {   // version 1
  public RussianDoll inner;

  public static void main(String args[]) {

    // This pair o' dolls is a paradox.  
    // Each contains the other.
    // If we don't want the user to be able to do this,
    // we'd better make "inner" a private field.

    RussianDoll rd1, rd2;
    rd1.inner = rd2;
    rd2.inner = rd1;
  }
}