Exams for a new student’s grade

Lists the exams a new student of one grade could be entered for on one olympiad, with the category, the sitting, the language and the fee: what find_exams_for_student offers a student of that grade who holds no exam yet, narrowed by this account’s country. Use it before register_students to turn the exam names on a registration sheet into exam ids, once per grade and olympiad on the sheet rather than once per student. session_date is the sitting’s calendar day (YYYY-MM-DD, no time and no time zone), and for a sitting run over more than one day, which its name shows, it is the last one. For a student already on the list, use find_exams_for_student instead.