library test;

class A {
  A f(A x, {A y}) {}
  A g(A x, {A y}) {}
  A h(A x, {A y}) {}
}

class B extends A implements I {
  f(x, {y}) {}
  g(x, {y}) {}
  h(x, {y}) {}
}

class I {
  I f(I x, {I y}) {}
  A g(I x, {I y}) {}
  A h(A x, {I y}) {}
}

main() {}