given any collection formula_16 of subsets of formula_1, there exists a unique dynkin system denoted formula_18 which is minimal with respect to containing formula_19. that is, if formula_20 is any dynkin system containing formula_19, then formula_22. formula_18 is called the dynkin system generated by formula_16. note formula_25. for another example, let formula_26 and formula_27; then formula_28.