library test;

abstract class A {
  int f(int x, int y);
  int g(int x, [int y]);
  int h(int x, {int y});
}

abstract class B {
  int f(int x);
  int g(int x);
  int h(int x);
}

abstract class C implements A, B {
  f(x, y);
  g(x, [y]);
  h(x, {y});
}

main() {}