c++ range-for loop over custom class ::begin() expects 1 argument, 0 provided

Question

I am following an example in section 7.2 of A Tour of C++ where I have a class which I want to iterate over in a range-for loop.

First, I have the parent.

template<typename T>
class Container {
    public:
        virtual T& operator[](int i) const = 0; 
        virtual int size() const = 0; 
        virtual ~Container() {} 
};

Second, I define the class itself. I define begin and end in order to iterate over the class in a range-for loop.

template<typename T>
class MyVector: public Container<T> {
public:
    explicit MyVector(int s); 
    MyVector(std::initializer_list<double>);
    T& operator[](int i) const override {
        if (i<0 || i>size()) throw std::out_of_range{"Anatoly's Vector operator []"};
        return elem[i];
        }
auto begin(MyVector<T>& x) -> T* const {return &x[0];}
auto end(MyVector<T>& x) -> T* const {return &x[0] + x.size();}
protected: 
    T* elem; 
    int sz;

Define the constructors:

template<typename T>
MyVector<T>::MyVector(int s) 
    :elem{new T[s]}, sz{s} // initialize members
{
    std::cout << "Default constructor called" << std::endl;
}

template<typename T>
MyVector<T>::MyVector(std::initializer_list<double> lst) // initialize with a list
:elem{new T[lst.size()]}, sz{static_cast<int>(lst.size())}
{
    std::copy(lst.begin(),lst.end(),elem); 
}
template<typename T>
auto MyVector<T>::size() const -> int { 
    return sz;
};

Finally, this is how I intend to use it:

void write2(MyVector<std::string>& vs) // Vector of some strings
{
    for (auto& s: vs) 
        std::cout << s << '\n';
}

But this doesn't compile. I get this compiler error:

In function 'void write2(MyVector<std::__cxx11::basic_string<char> >&)':
no matching function for call to 'MyVector<std::__cxx11::basic_string<char> >::begin()'
for (auto& s: vs)
note: candidate: 'T* MyVector<T>::begin(MyVector<T>&) [with T = std::__cxx11::basic_string<char>]'
candidate expects 1 argument, 0 provided

What am I doing wrong? Why candidate expects 1 argument, but 0 provided? How do I fix this?

EDIT: As commentators kindly suggested, begin should not take arguments, which explains the error message. I have misinterpreted the book, where begin is defined outside of the class: