1 / \ / \ 2 \ / \ \ 3 4 6 \ / / 5 / \ / \ / 7 DF(3) = {5} DF(4) = {5} DF(5) = {7} DF(6) = {7} Suppose a value is defined in 3 and 4 According to the notes, we insert phi nodes at 5 and 7, but that's wrong, no phi node is needed at 7