year(math, 60).
year(ai, 62).
year(english, 65).

str_rev(S, T) :- string_codes(S, SCODES), reverse(SCODES, TCODES), string_codes(T, TCODES).

can_register(STUDENT_ID, SUBJECT) :- str_rev(STUDENT_ID, REV_STUDENT_ID),
    sub_string(REV_STUDENT_ID, 0, 2, _, REV_YEAR_STR),
    str_rev(REV_YEAR_STR, YEAR_STR),
    number_string(YEAR, YEAR_STR),
    year(SUBJECT, REQ_YEAR),
    YEAR =< REQ_YEAR.