[lojban] Re: [lojban-beginners] Re: About the negators

["Jorge Llambías" <jjllambias@gmail.com>]

Here is a hopefully more clear restatement of the problem. Given {su'o
da na broda gi'e na brode}, we can rewrite it in purely prenex form as
follows:

  su'o da zo'u ge na ku zo'u da broda gi na ku zo'u de broda
  "There is some x which is neither broda nor brode."

Applying De Morgan's laws, we can move the negation through "ge",
changing it to "ga", and then through "su'o", changing it to "ro":

  na ku ro da zo'u ga da broda gi da brode
  "Not every x is broda or brode."

So far so good. I doubt anyone objecs to any of that. The original
"na"s can't be taken to have scope over "su'o" because "gi'e" will
block them.

Now let's consider just {su'o da na broda}. The obvious prenex
rewriting, if we hadn't read of any special rule, is:

  su'o da zo'u na ku zo'u da broda
  "There is some x  which is not broda."

  na ku ro da zo'u da broda
  "Not every x is broda."

which pretty much would agree with the case with "gi'e".

But for some inexplicable reason, the official rule is that in this
case "na" jumps over "su'o" without changing it, and "su'o da na
broda" has to be read as "no x is a broda".  The special scope rule
for "na" is not applicable in general, so why have it at all? Just to
make things complicated?

mu'o mi'e xorxes


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