function f<T, U>(y: T, y1: U, p: (z: U) => T, p1: (x: T) => U): [T, U] { return [y, p1(y)]; }
interface A { a: A; }
interface B extends A { b; }

var a: A, b: B;

var d = f(a, b, x => x, x => <any>x); // Type [A, B]