Clarification regarding auto to constant reference

In this code:

            int a=8; 
            const int &b = a;           //b is a Low-Level const
            auto c = b; 

I expected c to be constant reference type since it has been autoed to a low level const. But instead it is referring to a (which has been aliased by b) instead if b for its declaration.

c picks the b's type only when it is used like auto &c =b

What I understand is only top-level const is dropped. So can someone please explain what is wrong with my understanding?

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