Two different implementations of ÞR

[cgccuser]

There are currently two implementations of ÞR

1. Remove the last item of the cumulative sums of a list and prepend 0.
2. Reduce the rows of a by function b

I think the second is more general and worth keeping. The first is extremely specific.

(this was mentioned in the big bugs issue (test case [[]] : [0]))

[Steffan153]

I've used the first before (remove last of cumulative sums and prepend 0), so it can be useful. Reduce the rows of a by function b is useless, just vectorised reduce.

[lyxal]

Remove the last item of the cumulative sums of a list and prepend 0 seems like it should be kept because no need to have a digraph for vƒ