> This refers to Isabelle/e7c9a14632d0 and AFP/797f66d26443. > > * Abolished neg_numeral. > * Canonical representation for minus one is "- 1". > * Canonical representation for other negative numbers is > "- (numeral _)". > * When devising rule sets for number calculation, consider the > following cases: 0, 1, numeral _, - 1, - numeral _. > * Syntax for negative numerals is mere input syntax. > INCOMPATBILITY.
This also means that the set of numerals in non-canonical form has
increased: it does not contain only Numeral1 but also "- 0" and even
things like "- - - 2".
Currently HOLogic.dest_number recognizes all of these. Maybe this very
liberal semantics deserves reconsideration. Or maybe there should be
canonical normalizing conversion for numerals:
Numeral1 = 1
- 0 = 0
- - 1 = 1
- - numeral _ = numeral
Currently different packages have different opinions on that.
Florian
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