# Re: [isabelle] how to rewrite rule_tac x="A" in exI as tactic?

i forgot "val" in my attempt
val tac = let val x = @{term "A"} in rtac @{thm exI} 1 end
2012/1/25 Nils Jähnig <jaehnig at mi.fu-berlin.de>
> Hello,
>
> I was hoping that someone of you could give me a little help with tactics.
>
> I try to rewrite an apply-style proof into a tactic, for future
> automization.
>
> my goal:
> rewrite apply(rule_tac x="A" in exI) as a tactic
>
> my attempt:
> val tac = let x = @{term "A"} in rtac @{thm exI} 1 end
>
> my problem:
> the bound variable x is represented in another way, i.e. I'm substituting
> nothing with the let-in command.
>
> my questions:
> 1) could somebody tell me, how it will work
> 2) how can i display the internal representation of a theorem (on
> ML-level, so that i can see which term instead of x i need to substitute)
>
> thanks in advance
> Nils
>

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