# Re: ?? Functional Dependency Question ??

From: paul c <toledobythesea_at_oohay.ac>
Date: Tue, 21 Oct 2008 14:22:43 GMT
Message-ID: <TAlLk.2889\$fF3.1939_at_edtnps83>

```> On Oct 21, 8:15 pm, paul c <toledobythe..._at_oohay.ac> wrote:
```

>> David BL wrote:
>>
>> ...
>>
>>> RTP: (X->A)(Y->B) -> XY->AB
>>> (X->A)(Y->B) : premise
>>> X->A, Y->B : conjunction elimination
>>> XY : premise
>>> X,Y : conjunction elimination
>>> A : modus ponens on X,X->A
>>> B : modus ponens on Y,Y->B
>>> AB : conjunction introduction
>>> XY->AB : conditional proof
>>> (X->A)(Y->B) -> XY->AB : conditional proof
>> I can see that the second step is eliminating a "conjunction" but the
>> fourth step doesn't seem to me to involve a conjunction.
>
> Step 3: Premise XY (the conjunction of X and Y). ...

But XY (in the usual FD notation) is a union, not a conjunction.

(If step 4 is valid, there must be a subtlety here that goes beyond just conjunction elimination, ie., some other notion must be involved, but so far it could be eludes me.)

thanks,
p Received on Tue Oct 21 2008 - 16:22:43 CEST

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