@Override
    public BiMap<K, V> inverse() {
      return forward();
    }

    @Override
    public Set<V> keySet() {
      return new InverseKeySet();
    }

    private final class InverseKeySet extends Maps.KeySet<V, K> {
      InverseKeySet() {
        super(Inverse.this);
      }

      @Override
      public boolean remove(@CheckForNull Object o) {