Reference for Sanhedrin 150:13
למ"ד שריפה חמורה איכא למיפרך מה להיא שכן אמה בשריפה תאמר בהוא שאמו בסקילה
and just as the lower is assimilated to the upper in respect of punishment, so is the upper to the lower in respect of formal prohibition.<span class="x" onmousemove="('comment',' For in Lev. XVIII, 10, where the third lower generation is forbidden, nothing is said about punishment, which is derived from Lev. XX, 14, as stated above. On the other hand, in Lev. XX, 14, which is made to include the third generation above, though only explicitly stating the second, no formal prohibition is given. This in turn is derived from Lev. XVIII, 10. (Both are derived through the medium of Lev. XVIII, 17, the connecting link between the other two.) On Abaye's interpretation it is necessary to amend the Baraitha from 'and the lower is as the upper', to 'that the upper is as the lower etc.' ');"><sup>13</sup></span>