The first Correction (formation)
Rabbi Yitzchak draws a distinction between the rough hairs and the smooth hairs, the latter of which draw Chochmah to the brain of Zeir Anpin. He says that hairs must not bond to neighboring hairs, and that hair on the head must be long so that Chochmah can enter through the hair to the spinal cord that gets nourishment from the brain. We hear that all the hairs of the hair and beard of Arich Anpin are white as snow, while the beard of Zeir Anpin is black. Thirteen measures of mercy stem from the ancient Holy One, and corresponding to these there are thirteen measures in Zeir Anpin. We learn that if the thirteen Corrections (formations) of the beard of Arich Anpin had not existed neither the upper grades nor the lower grades would exist; children, longevity and sustenance depend on those Corrections (formations).