}
  }

  private interface Arithmetic extends Adder {
    int minus(int a, int b);
  }

  private static final class ForwardsToTheWrongMethod implements Arithmetic {
    private final Arithmetic arithmetic;

    ForwardsToTheWrongMethod(Arithmetic arithmetic) {
      this.arithmetic = arithmetic;
    }

    @Override
    public int minus(int a, int b) { // bad!

    }
  }

  private interface Arithmetic extends Adder {
    int minus(int a, int b);
  }

  private static final class ForwardsToTheWrongMethod implements Arithmetic {
    private final Arithmetic arithmetic;

    ForwardsToTheWrongMethod(Arithmetic arithmetic) {
      this.arithmetic = arithmetic;
    }

    @Override
    public int minus(int a, int b) { // bad!