# Re: [isabelle] few questions about Isabelle/jEdit

The color purple means that the proof method is still executing. If this is
still the case after 5 or so seconds, there is a good chance it will never finish.

All proof methods are sensitive to exactly how a you state a goal. Some more so
than others. What "algebra" can and cannot do is not so clear.

For proofs about real (in)equalities you could try (simp add: field_simps). It

Tobias

On 19/04/2014 18:41, noam neer wrote:
> hi,
> I have a few newbie questions about Isabelle/jEdit.
> I'm using version 2013-2 on Windows 7.
>
>
> 1. when I put the following in my theory file -
>
>        lemma NNF : "(1::real) < 0"
>        proof -
>            show ?thesis by auto
>        qed
>
>    the "by auto" part is colored in red,
>    and when I move the cursor to the end of its line
>    the output buffer shows some lines in red containing the message
>
>        Failed to finish proof:
>        ...
>
>    however, the lemma itself seems to be considered proven.
>    it can be printed with
>
>         thm NNF
>
>    and used in subsequent lemmas (such as proving "2<0").
>    why is this so? can I order Isabelle to stop at the first error and
> report?
>    alternatively, is there a way to get a report from Isabelle about those
> proofs that failed,
>    without having to scan the whole file myself for red spots?
>
>
> 2. here's an example of a more complex (and true) inequality with a proof -
>
>
>        lemma mon_mix_1 :
>            fixes a b c::real
>            shows "a*a + b*b + c*c >= a*b + a*c + b*c"
>
>        proof -
>
>            have tf3 :
>                 "(a-b)*(a-b)/2 + (a-c)*(a-c)/2 + (b-c)*(b-c)/2
>                  =
>                  a*a + b*b + c*c - a*b - a*c - b*c"
>            by algebra
>
>            have tf4 :
>                 "a*a + b*b + c*c - a*b - a*c - b*c
>                  =
>                  (a-b)*(a-b)/2 + (a-c)*(a-c)/2 + (b-c)*(b-c)/2"
>            using tf3
>            by auto
>
>            have tf5 : "a*a + b*b + c*c - a*b - a*c - b*c >=0"
>            using tf4
>            by auto
>
>            show ?thesis
>            using tf5
>            by auto
>
>        qed
>
>    when Isabelle reads this the "by algebra" part in the proof of "tf3" is
> colored purple,
>    but the output buffer seems to be OK, with no red or purple lines.
>    what does this mean ? is there an error in the proof ?
>
>
> 3. in the previous example, if I reverse the sides of the equality in "tf3"
>    the "by algebra" part is colored red and the output buffer contains some
> red lines
>    indicating failure. why does the order matter ?
>
>
> thanks, Noam.
>
>

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