Reference for Keritot 28:2

נהי דאיסור חל על איסור לית ליה איסור מוסיף ואיסור כולל אית ליה

- Although he generally holds that a prohibition cannot take hold where another prohibition exists, he admits that a prohibition which is more comprehensive or more extensive can take hold [of an already existing prohibition].<span class="x" onmousemove="('comment',' V. p. 104, nn. 6 and 7.');">²</span>

Jastrow