////////////////// interface Collection  //////////////////////////////

import java.util.Iterator;

interface Collection<E> extends Iterable<E>
{
  int size();
  boolean isEmpty();
  boolean contains(Object o);
  @Override
  Iterator<E> iterator();
  Object[] toArray();
  <T> T[] toArray(T[] a);
  boolean add(E e);
  boolean remove(Object o);
  boolean containsAll(Collection<?> c);
  boolean addAll(Collection<? extends E> c);
  boolean removeAll(Collection<?> c);
  boolean retainAll(Collection<?> c);
  void clear();
}