OLL 4
The algorithm, how to recognise it and how to practise it without cheating.
Recommended algorithm
f R U R' U' f' U F R U R' U' F'13 moves
Alternatives
(U) M U' r U2 r' U' R U' R' M'12 moves
How to recognise it
A dot with one yellow corner on top. Hold that corner at back right: the back side shows yellow only on its edge.
Its inverse is another case
Do the 4 algorithm backwards, F U R U' R' F' U' f U R U' R' f', and you are solving 3.
That's why CubeDojo never scrambles 4 that way: it builds a random state with the case fixed, so you practise 4 and not 3.
Practise 4 now
Random-state scrambles, a timer and spaced review. Free, on the web and on your phone.