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# Re: Programming is the Engineering Discipline of the Science that is Mathematics

Date: Sun, 11 Jun 2006 04:14:27 GMT
Message-ID: <DMMig.20488\$A26.470316@ursa-nb00s0.nbnet.nb.ca>

vc wrote:

> Keith H Duggar wrote:
> [Irrelevant stuff skipped]
>
> Assuming Bayesian treatment (which was not specified originally, mind
> you), the derivation is still meaningless. Let's try some argument
> from authority:

[snip]

``` > P(B|A) def P(A and B)/P(A)
>
> the requirement for such definition being that P(A) <>0,  naturally.

```

Keith used the equivalent definition:

P(A and B) = P(B|A)P(A), which places no requirements on P(A) because one does not divide by P(A).

In the case of P(A) = 0, P(A and B) = 0 and P(B|A) is indeterminate, which is to say, we don't care what it's value might be and it could be any real number; although, as a probability, we restrict it to real numbers in the range [0...1].

Thus, both of Keith's proofs were entirely valid because he neither inferred nor concluded using the indeterminate P(B|A). He made the valid conclusion that P(A and B) = 0 when P(A) = 0. Received on Sat Jun 10 2006 - 23:14:27 CDT

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