Ibn Qayyim "formulated evidential theories" that made judges "less reliant than ever before on the oral testimony." One example was the establishment of a child's paternity by experts scrutinizing the faces of "a child and its alleged father for similarities". Another was in determining impotence. If a woman sought a divorce on the grounds of her husband's impotence and her husband contested the claim, a judge might obtain a sample of the husband's ejaculate. According to Ibn Qayyim "only genuine semen left a white residue when boiled".