The process described is an equilibrium between two equivalents of an alkyl or aryl magnesium halide on the left of the equation and on the right side, one equivalent of the dialkyl or diaryl magnesium compound and magnesium halide salt.
The described process is an equilibrium reaction where two types of organomagnesium compounds are present in equal amounts, with one type being a dialkyl or diaryl magnesium compound and the other being a magnesium halide salt.