I had no idea that sort constraints played any role in the finding of theorems,
or why they should play a role. Whatever function they have in a search doesn’t
prevent the very similar query
dist norm "op=“
from picking up quite a few things. To my mind it’s quite unintuitive and maybe
should be looked at again.
Larry
> On 19 Nov 2015, at 09:21, Andreas Lochbihler <andreas.lochbih...@inf.ethz.ch>
> wrote:
>
> Hi Larry and Florian,
>
> the sort constraints for open, dist, and norm are changed in
>
> http://isabelle.in.tum.de/repos/isabelle/file/e89cfc004f18/src/HOL/Real_Vector_Spaces.thy#l1218
>
> These constraints were introduced by Brian Huffman in 2d91b2416de8 while he
> was reworking the type class hierarchy for topological spaces in 2009. I do
> not know his reasons for this, but I guess that they are meant to save type
> annotations.
>
> Best,
> Andreas
>
>
> On 19/11/15 10:10, Florian Haftmann wrote:
>> Hi Larry,
>>
>>> Andreas’s message reminds me that axioms of type classes are still not
>> picked up:
>>>
>>> class dist_norm = dist + norm + minus +
>>> assumes dist_norm: "dist x y = norm (x - y)”
>>>
>>> This item has the status of a theorem. However, the query
>>>
>>> dist "norm(_-_)”
>>>
>>> doesn’t find it. Surely it should?
>>
>> my mail from this summer still applies:
>>
>>> There is nothing wrong with type classes here:
>>>
>>> class involutory =
>>> fixes f :: "'a ⇒ 'a"
>>> assumes involutory: "f (f x) = x"
>>> begin
>>>
>>> lemma involutory3:
>>> "f (f (f x)) = f x"
>>> by (fact involutory)
>>>
>>> end
>>>
>>> find_theorems "f"
>>>
>>> It seems to be a constraint issue:
>>>
>>> find_theorems "_ = norm (_ - _)"
>>> ~> 'a::real_normed_vector is inferred
>>> find_theorems "_ = norm ((_::'a::dist_norm) - _)"
>>> ~> typing error
>>>
>>> Maybe some naughty tweaking of sort constraints or an unforseen
>>> behaviour of coercions, but these are mere guesses. I do not understand
>>> these parts of the type class hierarchy.
>>
>> I do not know why and how the default constraints of »dist« are changed,
>> but this is the basic cause for the behaviour you experience.
>>
>> Cheers,
>> Florian
>>
>>
>>
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