func apply<T, R>(_ x: T, _ f: (T) -> R) -> R { return f(x) } func sub(_ x: Int, _ y: Int) -> Int { return x - y } print(apply((4, 1), sub))func apply<T, R>(_ x: T, _ f: (T) -> R) -> R { return f(x) } func sub(_ x: Int, _ y: Int) -> Int { return x - y } print(apply((4, 1), sub))