>> 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the theory indeed is obsolete.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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