Error when trying initialize a set in a class

Question

I define a class named Quote and there is a multiset in it:

class Quote

{
public:
    Quote()=default;
    Quote(const std::string& book, double sales_price) :
        bookNo(book), price(sales_price) {}

    std::string isbn() const { return bookNo; }
private:
    std::string bookNo;
    static bool compare(const std::shared_ptr<Quote> &lhs, const std::shared_ptr<Quote> &rhs)
    {
        return lhs->isbn() < rhs->isbn();
    }
    std::multiset<std::shared_ptr<Quote>, decltype(compare)*>   items(compare);
protected:
    double price = 0.0;
    
};

But my IDE(Visual Studio) shows that function Quote::compare is not a type name

I usually initialize a set this way out of a class and it works well. Why that happens in a class? Thanks.