Q43

Consider two transactions $T_1$ and $T_2$, and four schedules $S_1, S_2, S_3, S_4$, of $T_1$ and $T_2$ as given below: $T_1: R_1[x]W_1[x]W_1[y]$ $T_2: R_2[x]R_2[y]W_2[y]$ $S_1: R_1[x]R_2[x]R_2[y] W_1[x] W_1[y] W_2[y]$ $S_2: R_1[x]R_2[x]R_2[y] W_1[x] W_2[y] W_1[y]$ $S_3: R_1[x]W_1[x]R_2[x] W_1[y] R_2[y] W_2[y]$ $S_4: R_2[x]R_2[y]R_1[x] W_1[x] W_1[y] W_2[y]$ Which of the above schedules are conflict-serializable?