Date: Thu, 6 Jun 2002 14:22:30 +0100
Reply-To: John Whittington <John.W@MEDISCIENCE.CO.UK>
Sender: "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From: John Whittington <John.W@MEDISCIENCE.CO.UK>
Subject: Re: Missing = zero; Immediate If?
In-Reply-To: <E17FqpG-0002zu-00@relay1.netnames.net>
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At 10:55 05/06/02 -0700, William W. Viergever wrote (in part):
>Methinks the Doc has his "modus ponens" ...If A then B. Thus given A then
>B... and his "modus tollens" ...If A then B. Thus not B then not A... confused.
>For ...If, and only If, A, then B. Thus given A then B *and* given B then
>A... i.e., it's a *biconditional* thingie <g>
No, that is not the source of the (or my) confusion. As I've indicated in
other messages, everyone else has seemingly been talking about something
different from me :-)
The rest of you are talking about logic and implication - in which sense I
obviously agree that 'if' and 'if and only if' are two very different animals.
However, (perhaps not totally unreasonably on SAS-L :-) I have been talking
about programming statements (in SAS or any other language).
Sig made my point much more succinctly that I have been doing. The
programming construct IF .... THEN is simply a programming construct,
allowing the conditional execution of one or more program expressions,
statements or command - and, except at the most simplistic level, has
nothing to do with logic or implication. Indeed, as I've pointed out, what
follows the 'THEN' may be a 'command' such as 'STOP' or 'OUTPUT' which
makes nonsense of any attempt to claim that there is, as a generalisation,
any logical/imputational meaning in such code.
... which leads me back to where I came in, namely my belief that, AS A
PROGRAMMING CONSTRUCT, a hypothetical IFF A THEN <statements> would have no
different functionality from the equivalent with IF.
However, I clearly owe lots of apologies, for having confused so many
people on SAS-L by talking about SAS programming statements, rather than
mathematical logic :-)
Kind Regards,
John
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