I read your medd lessons, and there is no medd al-farq (hamza succeeded by definite article [laam al-ta'reef]), is it in another lesson or is it part of another medd?
Answer
The term medd al-farq is a modern term not found in the early books of tajweed. It describes why the medd takes place, but it is not a separate category. The medd occurring when a noun starting with
preceded by a questioning hamzah ( 
of 
) is what is called by some modern books as medd al-farq, but it is already explained in
so there is no need for a separate category. Please see:
http://www.abouttajweed.com/the-mudood-the-lengthenings-/the-mudood-lengthenings-part-8.html
http://www.abouttajweed.com/hamzah-al-wasl/hamzah-al-wasl-lesson-8.html