Why using declaration is needed when an overload is deleted

Question

Why do I have to reintroduce the name of a function having some of its overloads deleted ?

#include <string>

struct A
{
    void f(int) {}
    void f(double) {}
    void f(const std::string&) {}
};

struct B : public A
{
    using A::f; // needed to compile : why ?
    void f(int)=delete;
    void f(double)=delete;
};

int main()
{
    B b;
    b.f(std::string("toto"));
}

Answer 1

A single declaration of f in the B class hides all declarations of f from the base A class.

And even marking the functions as deleted is considered a declaration.