Because the problem asked for it. We are to define methods on Object that already exist as Array methods. You can do it longhand or via this concise shortcut. End result is the same.

no longer relevant

I'm really embarrassed to have missed this elegant solution! 🤦😭

Interesting that [].all? 1 == true

You must say in the description that each solution [x, y, z] has to be sorted in decreasing order.
For example, the solution [13, 26, 13] has to be returned as [26, 13, 13]. I had to guess this...

Edit: However, I think it would be better to just keep the [x, y, z] order instead.

A kata don't have to be only implementation, it can be about thinking too.

1. Solved, I forgot to change that test
2. In Lisp, nil is the way to represent the 'false' boolean

Both sets of random tests use (expt n 2) and thus are essentially the same.
ng accepts nil as false.