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# [Frama-c-discuss] How to make wp to prove the invariant successfully?

• Subject: [Frama-c-discuss] How to make wp to prove the invariant successfully?
• From: pascal.cuoq at gmail.com (Pascal Cuoq)
• Date: Tue, 7 Feb 2012 06:01:34 +0100
• References: <CALiiei7XaT4q6C5-ij8=2wndqKE-NjShjw8DD0wJ=2OgF2uYKQ@mail.gmail.com>

```Hello,

On Tue, Feb 7, 2012 at 5:51 AM, Henry <njucslzh0714 at gmail.com> wrote:

>   x = 0;
>   z = 10;
>   /*@ loop invariant ? int x; x>=0;
>   */
>   while (x<=z) {
>     x++;
>   }
> Then the command "frama-c-gui -wp b.c" was executed. But I found that the
> status of the loop invariant was unknown because loop_inv_1_established
> could not decide. The proof obligation was:
> Goal store_phase_loop_inv_1_established:
>   forall x_0:int.
>   is_sint32(x_0) ->
>   (0 <= x_0)
>

The \forall quantifier in your invariant means that "x" in the rest of the
formula is not variable x from the program, but any int x.
You mean to talk about the variable x of the program. For instance, like
this:

/*@ loop invariant 0 <= x <= (z+1) ;
*/
while (x<=z) {
x++;
}

Frama-C Nitrogen with baseline Wp, together with alt-ergo 0.93, verify this
invariant.

Pascal
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