When the ketohexose, $\mathrm{D}\left(-\right)$ fructose is treated with phenyl hydrazine it produces an osazone that is identical with the one prepared from either $\mathrm{D}-\left(+\right)$ glucose or $\mathrm{D}-\left(+\right)$ mannose. How is the configuration of $\mathrm{D}\left(-\right)$ fructose related to those of $\mathrm{D}-\left(+\right)$ glucose and $\mathrm{D}-\left(+\right)$ mannose?