Re: circular relationships ok?

David Cressey wrote:
> "JOG" <jog_at_cs.nott.ac.uk> wrote in message
> news:1141480471.362482.59010_at_e56g2000cwe.googlegroups.com...
> > David Cressey wrote:
> > [snip]
> > >
> > > I think "A implies B" is the same as "B or not A".
> > >
> >
> > ? By "A implies B", he surely just means "if A then B". Or using
> > standard predicate logic notation "A -> B."

>

Hi David. Bit confused by your response. Originally you were talking about "B or not A" but then talk about "B^~A" which is "B and not A". (I'll take the second as a typo). The distinction is:

A -> B is a proposition
B v ~A is a boolean expression

The first is a declared fact, the second just a boolean statement that resolves to true or false, obviously a very different kettle of fish. So I thought that you might perhaps have meant "B v ~A = True", but substituting a couple of values in for A and B highlights there still exists a difference:

A -> B
IF it is raining THEN I wear a coat

B OR ~A = True
EITHER I wear a coat OR it is NOT raining

These are clearly very different things. For example, in the second statement I have declared that I will not be wearing a coat if it is dry but very cold outside, however this would be a perfectly acceptable state of affairs according to the first statement.

All best, Jim. Received on Sat Mar 04 2006 - 18:56:32 CET