Some/many rules can be used both ways. For example, in propositional logic we have

  A10 : Impl(x, y) -> Or(Not(x), y)
  A11 : Or(Not(x), y) -> Impl(x, y)

It would be more attractive to be able to write

  A10 : Impl(x, y) <-> Or(Not(x), y)

then, A10L would refer to the first rule and A10R to the second

-- EelcoVisser - 27 Oct 2001

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CategoryToDo^? | LanguageExtensions