为什么这个代码能过？！求语法解析

#include<iostream>
using namespace std;
using ____=decltype(1);
using __________=std::ostream;
using ___________=std::istream;
template<typename T>
concept ________=requires(T a){
    cout << a;
};
template<typename T>
concept _______=requires(T a){
    cin >> a;
};
template<typename T>
concept _________=is_integral_v<T>||requires(T a,T b){
    (a^b|a&b|(a&b)<<1);
};
template<_________ T>
const T _(const T &a,const T &b){
//  cout << "a=" << a << ", b=" << b << ".\n";
    if(b==0){
        return a;
    } else{
        return _((a^b),((a&b)<<1));
    }
}
__________ &_____(__________ &os){
    return os;
}
template<________ T>
__________ &_____(__________ &os,const T &val){
    return (os << val);
}
template<________ T,________... Args>
__________ &_____(__________ &os,const T &val,const Args& ...args){
    return ______(______(os,val),args...);
}
___________ &______(___________ &is){
    return is;
}
template<_______ T>
___________ &______(___________ &is,T &val){
    return (is >> val);
}
template<_______ T,_______... Args>
___________ &______(___________ &is,T &val,Args& ...args){
    return ______((______(is,val),is),args...);
}
int main(){
    ____ __,___;
    ______(cin,__,___);
    _____(cout,_(__,___));
    return 0;
}

提交选择C++20即可通过，但里面用到了什么东西？？没看懂