Cannot redefine `bool` and `tt`

[FissoreD]

Not sure whether this is a real bug, but I would like to define a
self-contained program, i.e., without relying on the ELPI standard library.
I would like to redefine the bool type with its constructors.

The file looks like:

% main.elpi
kind bool type.
type tt bool.    % The error is at this line
type ff bool.

However, when I execute the command elpi main.elpi -test, I get the
following error:

Incompatible provenance for symbol ff: Ast.Structured.Elpi !=
(Ast.Structured.OCaml Ast.Structured.Builtin {variant = 1})

Is this expected, or should the compiler understand that adding
tt to bool is a no-op, since tt already exists as
a constructor of bool in the standard library?

Moreover, what I find weird is that I can create type tt int -> bool without warnings

[gares]

For the first issue, there is no way to unload the standard library