Most likely it is something very easy I am missing but searched carefully the manual and couldn’t find a function to “de-vectorize” a vector of strings

Starting let’s say with

`a = ["X", "Y", "Z"]`

`b = [a]`

now `b == [["X", "Y", "Z"]]`

. I would like to find a function `f(.)`

such that

`b[f(a)] = a`

or `f(["X", "Y", "Z"]) = "X", "Y", "Z"`

Thank you for your help