CREATE TABLE table_204_790 (id NUMBER, "year" NUMBER, "nw rank" NUMBER, "venue" CLOB, "opp rank" NUMBER, "opponent" CLOB, "score" CLOB, "w/l" CLOB, "round" CLOB, "notes" CLOB)

who was an opponent in 1996 and 1997 ?
SELECT "opponent" FROM table_204_790 WHERE "year" = 1996 INTERSECT SELECT "opponent" FROM table_204_790 WHERE "year" = 1997
SELECT "opponent" FROM "table_204_790" WHERE "year" = 1996 INTERSECT SELECT "opponent" FROM "table_204_790" WHERE "year" = 1997