class Foo<X> {}

class Bar<X, Y> {}

extension A1 on dynamic {}

A1 foo1(A1 a) => throw 42;

extension A2<X> on Foo<X> {}

A2 foo2(A2<int> a, A2 ai) => throw 42;

extension A3<X, Y extends Function(X)> on Bar<X, Y> {}

A3 foo3(A3<int, Function(num)> a, A3 ai) => throw 42;

extension A4<X, Y extends Function(X)> on Foo<Y> {}

A4 foo4(A4<int, Function(num)> a, A4 ai) => throw 42;
bar() {}
main() {}