I have seen many qurraa merge the "laa" into the "raa" as well, but this is not listed under the letters that merge on the lessons

Question
Salaamun 'Alaykum wa Rahmatullah,
Jazakallah for your online lessons regarding the science of Tajweed. I was reading the following article: http://www.abouttajweed.com/the-two-same-similar-close-and-far/the-two-the-same- the-two-similar-the-two-close-and-the-two-far-p.html

I have seen many qurraa merge the "laa" into the "raa" as well, but this is not listed under the letters that merge. An example where it is done is in the last verse of Surah Mu'minoon. Would this also fall under the heading of Idghaam al-Mutajaanisaan, or is it some other rule?
Jazakallahu Khairan and wassalaam.

Answer
Wa alaikum assalaam wa rahmatullahi wa barakaatuh
Wa iyyaakum. 
Due to an error when transferring the old site information to the new site, there are some missing lessons in the section on letter relations and idghaamaat. These can be found at:
http://www.abouttajweed.com/al-mutamathilayn_al-mutajaanisayn_4.htm

http://www.abouttajweed.com/al-mutamaathilayn_al-mutajaanisayn_al-mutaqaaribayn5.htm

http://www.abouttajweed.com/al-mutamaathilaan_al-mutajaanisaan_al-mutaqaaribaan_6.htm

The particular lesson you are looking for is number 5.  The relationship of of the and is mutaqaaribayn. 
Wa iyyaakum.  Wa assalaam alaikum wa rahmatullah.