Questions about ”operator=” and ”operator[]”

Question

I have a question about the code below.

Why is it possible to run const auto& vec1 = vec; successfully even though my_vector& operator=(const my_vector&) = delete is defined?

Secondly, why is the &, && at the end of operator[] necessary? If I remove them, I get an error.

I understand that the & after the operator is a reference to the class itself. Then I grasp that the ones without const are for writing.

#include <iostream>
#include <stdlib.h>
#include<vector>

template<typename T, typename Alloc = std::allocator<T>>
class my_vector
{
  std::vector<T, Alloc> vec;

public:
  my_vector(const my_vector&);
  my_vector& operator=(const my_vector&) = delete;
  my_vector(std::initializer_list<T> init) : vec{init} {}
  T& operator[](std::size_t n) & { std::cout<<"&"<<std::endl; return vec[n]; }
  const T& operator[](std::size_t n) const& { std::cout<<"const &"<<std::endl;  return vec[n]; }
  T operator[](std::size_t n)  && noexcept {std::cout<<"move"<<std::endl; return std::move(vec[n]); } 
};

int main()
{
    my_vector<int> vec{1, 2, 3};
    
    const auto& vec1 = vec;
    vec[0] = 2; //case1 &
    std::cout<<vec1[0]<<std::endl;
    //vec1[0] = 1; const error
    int tmp1 = vec1[0] ; //case2 const&
    auto&& vec5 = my_vector<int>{1, 2, 3}[0]; //case3 move
}