// @dart = 2.9
typedef F<X> = void Function<Y extends X>();
F<X> toF<X>(X x) => null;
typedef Fcov<X> = X Function();
typedef Fcon<X> = Function(X);
typedef Finv<X> = X Function(X);
typedef FcovBound<X extends num> = X Function();
typedef FconBound<X extends num> = Function(X);
typedef FinvBound<X extends num> = X Function(X);

class A<X> {}

typedef FcovCyclicBound<X extends A<X>> = X Function();
typedef FconCyclicBound<X extends A<X>> = Function(X);
typedef FinvCyclicBound<X extends A<X>> = X Function(X);
typedef FcovCyclicCoBound<X extends Function(X)> = X Function();
typedef FconCyclicCoBound<X extends Function(X)> = Function(X);
typedef FinvCyclicCoBound<X extends Function(X)> = X Function(X);

class B<X> {}

void testTopLevel() {}
void testNested() {}
main() {}