CREATE TABLE table_45646 ("Position" FLOAT, "best year" TEXT, "best 2-year period" TEXT, "best 3-year period" TEXT, "best 5-year period" TEXT, "best 10-year period" TEXT, "best 15-year period" TEXT)

Which best 10-year period has a best 2-year period of petrosian?
SELECT "best 10-year period" FROM table_45646 WHERE "best 2-year period" = 'petrosian'
SELECT "best 10-year period" FROM "table_45646" WHERE "best 2-year period" = 'petrosian'