Although this naive concat function cannot operate on objects, Z.concat and S.concat can do so. concat ({}) ({}) is thus a confusing example: it is a logical operation but it is not supported due to a shortcoming. concat (null) (null) is clearer.
Do these changes remove some of the confusion, @jeanbaptiste-brasselet?
See #193
Commit message:
Do these changes remove some of the confusion, @jeanbaptiste-brasselet?