This is the third installment in the tough/hard/weird/nonintuitive F2L series, with the first and second posts among the most popular on this site and my Youtube channel. These cases (#1518) require splitting toplayer pairs before recombining them — what the F2L wiki refers to as “splitting pairs by going over.” As with the cases in the other tutorials, having now spent some time with alternate algorithms, these seem less “tough” than just nonintuitive.
Following the format of the previous installments, here’s a video tutorial, followed by table contrasting my old (intuitive) approaches against the improved ones:
CASE  OLD/SETUP  IMPROVED 
#15 
y’ (R’ U R) U2 y (R U R’) (R U’ R’) U’ (F R’ F’ R’) U’ 
U (R’ F R F’) U (R U R’)

#16 
(R U’ R’) U2 y’ (R’ U’ R) (F’ U F) U2 (R U R’) 
M U’ (R’ F R) U M’ [y’] (R U’ R’) U2 (F’ U’ F) 
#17 
(R U2′ R’) U’ (R U R’) (R U’ R’) U (R U2 R’) 
(R U2 R’) U’ (R U R’) 
#18 
y’ ( R’ U2 R) U (R’ U’ R) (R’ F R F’) U (R U’ R’) U (R U’ R’) 
(R U R’ U’) (R U R’ U’) F R’ F’ R 
* setups (inverses) written in red
The chore of keeping all these algorithms separated in my mind continues to grow more difficult….
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