dduan

struct Complex<T: FloatLiteralConvertible> {
    var real: T
    var imaginary: T
}

func +(lhs: Complex<Double>, rhs: Complex<Double>) -> Complex<Double> {
    return Complex<Double>(real: lhs.real + rhs.real, imaginary: lhs.imaginary + rhs.imaginary)
}

func -(lhs: Complex<Double>, rhs: Complex<Double>) -> Complex<Double> {