type EvenOdd {
  bool even(int);
  bool odd(int);
}

// The following class tests mutually recursive methods.

class EvenOddC() : EvenOdd impl EvenOdd {
  bool even(int n) {
    cond {
      n == 0 => return true;
      n < 0  => return even(-n);
      else      return odd(n - 1);
    };
  }
  bool odd(int n) {
    cond {
      n == 0 => return false;
      n < 0  => return odd(-n);
      else      return even(n - 1);
    };
  }
  export EvenOdd : even, odd;
}