[isabelle] Hidding the "int", "nat" and "real" conversion functions

I want to hide the "int", "nat" and "real" conversion functions when
Isabelle outputs an term. So that a term like 
"nat (x * int y - f (int z))" gets written as "x * y - f z" human users
are usually capable of interfering the correct conversion functions.

First I tried to just add a translation:
> translations
>  "N" <= "of_nat N" (* "int" do not work, it is represented as "of_nat" internally *)

> term "int 1 + 2"
> (* output: "2"  HUH! *)

This breaks the entire output process! Is this a bug in the pretty
printer or should I just not add this translation. In OptionalSugar the
same is done with the "set :: 'a list => 'a set" conversion function!

As alternative I'm currently using a notation:

> notation (output) int ("_" 70)
> term "x * int (a + b) + f (int a)"
> (* output: "x * (a + b) + f (a)" *)

This nearly works, but I don't get rid of the parenthesis around the
function parameter. I tried several other precedencies but no one
worked. There are parenthesis around the function parameter or the
parenthesis around the addition are missing.

Has anyone a solution to this problem?

   Johannes Hölzl

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