Re: [isabelle] More use of "-" and "!" in isabelle 2009-1?



Hi Rafal,

> Regarding "-" and fact chaining issues, it turns out that the pre-2009
> Isabelle does warn me that this is a legacy feature:
>     "Legacy feature! Implicit use of prems in assumption proof"
> I just don't really get why this is, and how I should be writing my
> proof instead, what the "sanctioned" way is.

The "prems" are, roughly, the accumulated facts within a proof, which as
a historical accident have been used implicitly by certain proof methods
-- which, following the rule of thumb "explicit is better than
implicit", turned out as a bad idea.  You can recover this behaviour by
using prems explicitly, e.g. "using prems by ..." or "by (auto simp add:
prems)" etc.  Best practice is to refer to used facts implicitly;
recall that you can quote facts by proposition using backticks ``.

Hope this helps,
	Florian

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