[isabelle-dev] Obsolete numeral experiments?

[Florian Haftmann]

>> http://isabelle.in.tum.de/repos/isabelle/file/6324f30e23b6/src/HOL/ex/Binary.thy
>> http://isabelle.in.tum.de/repos/isabelle/file/6324f30e23b6/src/HOL/ex/Numeral_Representation.thy
>>
>> Can we delete that, and keep the history inside the history? Or are there
>> remaining aspects that are not in the official numeral implementation (and
>> reform) by Brian Huffman?
> 
> Numeral_Representation.thy defines a couple of type classes for
> subtraction that were never added to the main libraries:
> semiring_minus and semiring_1_minus. (I believe these were Florian's
> work.) They would let us generalize some rules that are currently
> specific to nat. We should discuss whether these (or some variation)
> would be appropriate to add to Groups.thy before we delete
> Numeral_Representation.thy.

I have some plans in the drawer to introduce / refine type classes for
»confined subtraction« coverting natural numbers and multisets.  There I
will reconsider semiring_minus and semiring_1_minus.  The remainder of
the theory indeed is obsolete.  I guess there are subtle and not so
subtle differences between that concept and the now existing
implementation, but I do not worry much about that, since the
implementation resolves the ancient central problem of signed numerals
and is just working.

	Florian

-- 

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