C++ - Can't pass reference to reference (value assign is implied)

refernce_to_reference_implies_value_assign.cpp

struct foo {
    foo& operator=(const foo& other) = delete; // foo is not copy-assignable
};

void bar() {
    foo f1;
    foo& r1 = f1; // Ok. r1 is reference to f1.
    foo& r2 = r1; // ok. r2 is refernce to r1 which is semanticly the value f1.
    r2 = r1; // Error. Semantics implies value assign (although both sides are references) and foo instance f1 is not assignable. 
    
    // Pass refernce round with http://en.cppreference.com/w/cpp/utility/functional/reference_wrapper
    std::reference_wrapper<foo> rw1 = f1; // Ok. rw1 models a foo reference to f1.
    std::reference_wrapper<foo> rw2 = rw1; // ok. rw2 models a foo refernce with the same value as rw1 (refernce to same value f1)
    rw2 = rw1; // Ok. The refernce held by rw1 is passed to rw2 (value f1 not mutated)
    
    r2 = rw2; // Error. r2 is semanticly alias for value refernced by r1 which is f1 (assign to f1 attemted)
    
}