A Groszek-Laver pair of undistinguishable $E_0$ classes
A generic extension $L[x,y]$ of $L$ by reals $x,y$ is defined, in which the union of $\mathsf E_0$-classes of $x$ and $y$ is a $Π^1_2$ set, but neither of these two $\mathsf E_0$-classes is separately ordinal-definable.
math.LO↗