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#define NLEN 30struct book{        int isbn;        char name[NLEN];        char auther[NLEN];        char publisher[NLEN];        struct user *hasMe;        struct book *left;        struct book *right;};struct user{        int id;        char name[NLEN];        char address[NLEN];        struct book *borrowed;        struct user *next;        struct user *prev;};int main(){}