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