interface IA<T> {}

interface IB : IA<int>{}

class C : IB, IA<long>
{
    static void Main()
    {
        C c = new C();
        Foo(c); // error CS0411: The type arguments for method 'C.Foo<T>(IA<T>)' cannot be inferred from the usage. Try specifying the type arguments explicitly.
    }

    static void Foo<T>(IA<T> x) {}
}