[josevalim]

For the paper, we have decided to go as precise as possible, since its goal is to discuss the type-system semantics and not its syntax, so parentheses are everywhere.

You will for sure be able to drop the outer parens in your case and you _may_ be able to drop them on the function types too (to be decided). Ending up with something like this:

    $ (integer -> integer) and (true -> false) and (false -> true) and (a -> a) when a: not(integer or boolean)
    def negate(arg)

We will also allow intersections to be broken across multiple declarations:

    $ integer -> integer
    $ true -> false
    $ false -> true
    $ a -> a when a: not(integer or boolean)
    def negate(arg)