P92. Consider two multiplicative subsets D and E a commutative ring R satisfying D g B. Let go: R[D'1] r RUE1] be the ring homomorphism defined, for any fraction NC! in R[D'1], by $(rfd) = rid. Prove that the following statements are equivalent: (a) The map 90 is a ring isomorphism. (b) For any.r element 9 in E, the fraction all is a unit in R[D1]. (c) For any element 9 in B, there exists an element 3 in R such that as E D