[isabelle-dev] not-exists problem
makarius at sketis.net
Tue Sep 13 20:56:54 CEST 2016
On 13/09/16 01:46, Lawrence Paulson wrote:
> We have a problem with the ∄ operator, when existential quantifiers are nested:
> lemma "(∄x. ∃y. P x y) = (~(∃x y. P x y))"
> by (rule refl)
> Note that ∄x y. P x y would be fine.
Looking briefly over this thread, my impression is that the simplest
solution is to disallow multiple variables for
∄ and ∃! as well.
We already have special quantifiers like ∃x:A that cannot be repeated
(for very basic technical reasons). This means users are used to
non-iterated quantifiers: it should cause less surprise than extra
syntax that is unclear.
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