Slashes are tricky, ideally you want both last axis/first axis versions (imo) as they're convenient and more mnemonic than ⍤¯1.

There are two ideal forms of reduce, insert & fold which apply f between the elements (depth-1 sub-arrays) and major cells (rank-1 sub-arrays).

One could also want to supply an initial element to fold as a left argument (instead of n-wise reduction), and avoid identity elements.

Providing foldl is also an option.

All in all, you're looking at 8/9 different operators...

A nice little challenge I found on the internet. Probably already known to you, but found it fun to puzzle it out.

The challenge is to write a series of expressions using the year (in this case 2021) to return each number from 0-100, meaning an expression per number. Each expression must contain the digits of the year in order and include no other digits. The digits from the year can be grouped together or separated using spaces, decimals or any functions or operators you wish to use, for example: 2021, 20+21, 2.021, 2 0 2 1.