6:36 `void registerStudent(const Student & const student_input)`error

안녕하세요, const를 두번 넣으니까 아래와 같은 에러가 나옵니다. 이렇게 바꾸면 문제가 없습니다. const Student & student_input
const가 2개 필요한 이유가 따로 있을까요?

/usr/bin/clang++ -std=c++17 -fcolor-diagnostics -fansi-escape-codes -g /Users/user/Documents/cpp/10-3/10-3.cpp -o /Users/user/Documents/cpp/10-3/10-3
In file included from /Users/user/Documents/cpp/10-3/10-3.cpp:4:
/Users/user/Documents/cpp/10-3/Lecture.h:26:40: error: 'const' qualifier may not be applied to a reference
    void assignTeacher(const Teacher & const teacher_input)
                                       ^
/Users/user/Documents/cpp/10-3/Lecture.h:31:42: error: 'const' qualifier may not be applied to a reference
    void registerStudent(const Student & const student_input)

code

# Lecture.h
#pragma once

#include <vector>
#include "Student.h"
#include "Teacher.h"

class Lecture
{
private:
    std::string m_name;

    Teacher teacher;
    std::vector<Student> students;

public:
    Lecture(const std::string & name_in)
        : m_name(name_in)
    {}

    ~Lecture()
    {
        // do NOT delete teacher
        // do NOT delete students
    }

    void assignTeacher(const Teacher & const teacher_input)
    {
        teacher = teacher_input;
    }

    void registerStudent(const Student & const student_input)
    {
        students.push_back(student_input); // vector에 넣는다
    }

    void study()
    {
        std::cout << m_name << " Study " << std::endl << std::endl;

        for (auto & elem : students) // for each에서 ref로 받아야 값 변환 가능
            elem.setIntel(elem.getIntel() + 1);
    }

    friend std::ostream & operator << (std::ostream & out, const Lecture & lecture)
    {
        out << "Lecture name : " << lecture.m_name << std::endl;
        out << lecture.teacher << std::endl;

        for (auto elem : lecture.students)
            out << elem << std::endl;
        
        return out;
    }
};