Notes & justification
Two identical letters meeting across two words must be merged, the first into the second — al-Sūsī's idghām kabīr. See vol. 1, p. 14.
Whatever two identical letters stand in two separate words — the first of them must be merged.
The lām merges into a following rāʾ (though not the reverse) when both are fatḥah-bearing after a sākin — hence faʿal rabbuka. See vol. 1, p. 45.
The rāʾ merges into the lām and it into the rāʾ, but both are kept clear when the two open vowels follow a quiesced letter — save as transmitted.