Halakhah for Sanhedrin 151:12
למ"ד סקילה חמורה איכא למיפרך מה להוא שכן אמו בסקילה תאמר בהיא שאמה בשרפה
Whilst on the view, 'judge from it and place it on its own basis,' [the deduction would proceed thus:] just as his daughter-in-law is forbidden him, so is her daughter-in-law forbidden; and place it on its own basis, thus: in the former case, [his daughter-in-law] the punishment is stoning; but in the latter, burning, the punishment we find for incest with her mother. But if stoning is severer, this can be refuted. [Thus]: Why is his daughter-in-law forbidden? Because his mother is forbidden him on pain of stoning. But can you say the same of her daughter-in-law, seeing that her mother is forbidden only on pain of burning! Moreover, just as in his case, you draw a distinction between his daughter [punished by burning] and his daughter-in-law [by stoning], so in her case, you should draw a distinction between her daughter and her daughter-in-law.<span class="x" onmousemove="('comment',' I.e., Just as the punishment for his daughter-in-law is severer than for his daughter, viz., stoning instead of burning, so her daughter-in-law should be more stringently interdicted than her daughter, viz., by stoning, instead of burning. But if we compare her daughter-in-law to her mother, the punishment is burning. Hence the entire deduction is impossible. ');"><sup>12</sup></span>