Ошибка E0349: отсутствует оператор

#include <iostream>
#include <fstream>
#include <algorithm>
#include <string>
using namespace std;
class Contingent {
protected:
    string firstname, lastname;
    int age;
public:
    Contingent(string, string, int);
    Contingent() {}
    ~Contingent();
    friend istream& operator>>(istream&, Contingent&);
    friend ostream& operator<<(ostream&, Contingent&);
};
ostream& operator<<(ostream& os, Contingent& con)
{
    os << " saxeli " << con.firstname << endl;
    os << " gvari " << con.lastname << endl;
    os << " asaki " << con.age << endl;
    return os;
}
istream& operator>>(istream& is, Contingent& CON)
{
    cout << " shemoitanet saxeli da gvari " << endl;
    is >> CON.firstname >> CON.lastname;
    cout << " ramdeni wlisaa ? " << endl;
    is >> CON.age;
    return is;
}
Contingent::Contingent(string fname, string surname, int age) :firstname(fname), lastname(surname), age(age) {}
Contingent::~Contingent() = default;
class HeightSchool {
protected:
    string name;
    int departments;
public:
    HeightSchool(string, int);
    ~HeightSchool();
    string get_name();
    HeightSchool() {}
    friend istream& operator>>(istream&, HeightSchool&);
    friend ostream& operator<<(ostream&, HeightSchool&);
};
string HeightSchool::get_name()
{
    return name;
}
ostream& operator<<(ostream& os, HeightSchool& hsc)
{
    os << " dasaxeleba " << hsc.name << endl;
    os << " fakultetebis ricxvi " << hsc.departments << endl;
    return os;
}
istream& operator>>(istream& in, HeightSchool& HS)
{
    cout << " shemoitanet  dasaxeleba da fakultetebis raodenoba " << endl;
    in >> HS.name >> HS.departments;
    return in;
}
HeightSchool::HeightSchool(string nm, int dp) :name(nm), departments(dp) {}
HeightSchool::~HeightSchool() = default;
class Bachelor :public Contingent, public HeightSchool {
private:
    string specialty;
    int grade;
public:
    Bachelor(string, string, int, string, int, string, int);
    Bachelor() {}
    ~Bachelor();
    bool operator<(Bachelor&);
    friend istream& operator>>(istream&, Bachelor&);
    friend ostream& operator<<(ostream&, Bachelor&);
    friend bool compare(Bachelor&, Bachelor&);
};
bool Bachelor::operator<(Bachelor& lp)
{
    return this->name < lp.name;
}
ostream& operator << (ostream& os, Bachelor& bch)
{
    os << (Contingent&)bch <<
        (HeightSchool&)bch << endl;
    os << " specialoba " << bch.specialty << endl;
    os << " shefaseba " << bch.grade  << endl;
    return os;
}
istream& operator>>(istream& in, Bachelor& fr)
{
    in >> (Contingent&)fr >> (HeightSchool&)fr;
    cout << " shemoitanet  specialoba " << endl;
    in >> fr.specialty;
    cout << " shemoitanet shefaseba " << endl;
    in >> fr.grade;
    return in;
}
bool compare(Bachelor& bch, Bachelor& les)
{
    return les < bch;
}
Bachelor::Bachelor(string fname, string surn, int a, string name, int b, string spec, int grade) :Contingent(name, surn, a),
HeightSchool(name, b), specialty(spec), grade(grade) {}
Bachelor::~Bachelor() {}
void fillaray(Bachelor* arr, int& n)
{
    ifstream ifs("bachelor.txt");
    while (!ifs.eof())
    {
        ifs >> arr[n++];
    }
    ifs.close();
 
}
int main()
{
    static Contingent cn("Guga", "Apkhazava", 2010);
    static HeightSchool hs("Komarovi", 15);
    cout << " davbechdot informacia mat shesaxeb" << endl;
    cout << cn << endl << endl << hs << endl;
    Bachelor* bc = new(nothrow)Bachelor[1200];
    if (bc == nullptr) { cout << " mexsiereba ver gamoiyo " << endl; return 0; }
    int curentlysize = 0;
    fillaray(bc, curentlysize);
    sort(bc, bc + curentlysize, [](Bachelor& a, Bachelor& b) {return  b < a; });
    for (int i = 0; i < curentlysize; i++)
    {
        cout << bc[i];
    }
    Bachelor min = bc[0];
    Bachelor max = bc[0];
    string sum = bc[0].get_name();
    for (int i = 1; i < curentlysize; i++)
    {
        sum += bc[i].get_name();
        if (bc[i].get_name() < min.get_name())min = bc[i];
        if (bc[i].get_name() > max.get_name())max = bc[i];
    }
    float avarage = sum / curentlysize;
    int index = 0;
    for (int i = 0; i < curentlysize; i++)
    {
        if (bc[i].get_name() <= avarage) {
            index = i; break;
        }
    }
    Bachelor axlos;
    if (bc[index + 1].get_name() - avarage < bc[index - 1].get_name() - avarage) { axlos = bc[index + 1]; }
    else axlos = bc[index - 1];//vedzebt isets romelta shoris   diapazonic umoklesia;
    if (axlos.get_name() > bc[index].get_name() - avarage)axlos = bc[index];
    ofstream os("report.txt");
    os << "minimaluri aris " << min.get_name() << " maqsimaluri aris " << max.get_name() << "  sashualoze yvelaze axlos aris " << axlos.get_name() << endl;
    delete[]bc;
    bc = nullptr;
}