F2L 4
The algorithm, how to recognise it and how to practise it without cheating.
Recommended algorithm
R U R'3 moves · R and U only
How to recognise it
Corner above the slot with white facing right; the edge is at the back, its top colour matching the corner's front sticker.
Its inverse is another case
Do the 4 algorithm backwards, R U' R', and you are solving 1.
That's why CubeDojo never scrambles 4 that way: it builds a random state with the case fixed, so you practise 4 and not 1.
Practise 4 now
Random-state scrambles, a timer and spaced review. Free, on the web and on your phone.