no + or - defined for fixed point types in Standard, why ?

[Mehdi Saada <00120260a@gmail.com>]

I have to define the addition, substraction and multiplication operators for a fixed point real type, and (though I KNOW you don't do, that, but pass use a parent type whose primitives have not been overrided) I tried to prefix by "Standard" to see what happens. I thought it would just not work.
I got that:
p_proba1.adb:11:37: warning: instance does not use primitive operation "+" at p_proba1.ads:8
p_proba1.adb:11:37: warning: instance does not use primitive operation "*" at p_proba1.ads:12
p_proba1.adb:11:37: warning: instance does not use primitive operation "-" at p_proba1.ads:16
p_proba1.adb:43:16: "-" not declared in "Standard"

I could see that + and - weren't defined for universal_fixed in Standard, though they are indeed, hum, defined in real life. What does it mean ?

Here's my type definitions:

   type T_proba is private;
private
   type Modele is delta 0.001 range 0.0..1.0 with Small => 0.001; -- to style have at hands primitives for fixed point types.
   type T_proba is new MODELE; -- what I know I should use (but it still say "instance blablabla"

And in the body, to define the operation, I convert to Modele.
But I got those warnings:
p_proba1.adb:11:37: warning: instance does not use primitive operation "+" at p_proba1.ads:8
p_proba1.adb:11:37: warning: instance does not use primitive operation "*" at p_proba1.ads:12
p_proba1.adb:11:37: warning: instance does not use primitive operation "-" at p_proba1.ads:16

Is there another way to refer to the T_proba's primitive operations ? And why does it upset the compiler ?
I try to add "overriding" to these three operations, since I read it was a good practice, and I only got one more error: "subprogram "*" is not overriding"...

I just read the course's parts on numerics, and I admit I didn't get most of it, by far. Was much much harder to me, than Ada proper. But I don't remember, and can't find info on any of these points...


My operators' definitions:
   function "*"
     (Un,                   
         Deux : in     T_Proba)
      return T_Proba is (Standard."*"(Un, Deux));
   function "+"
     (Un,                   
         Deux : in     T_Proba)
        return T_Proba is ((-Un) * (-Deux));
   function "-"
     (Un : in     T_Proba)
      return T_Proba
   is (Standard."-"(1.0 - UN));

ps: remember, I KNOW it's wrong. but I wonder why exactly.