OLL 31
The algorithm, how to recognise it and how to practise it without cheating.
Recommended algorithm
R' U' F U R U' R' F' R9 moves
How to recognise it
A P shape: the right column and the back edge. The left side shows yellow only on its edge.
Its inverse is another case
Do the 31 algorithm backwards, R' F R U R' U' F' U R, and you are solving 40.
That's why CubeDojo never scrambles 31 that way: it builds a random state with the case fixed, so you practise 31 and not 40.
Practise 31 now
Random-state scrambles, a timer and spaced review. Free, on the web and on your phone.