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All arrays can be adjustable?
- To: "David C. Plummer" <DCP@SCRC-QUABBIN.ARPA>
- Subject: All arrays can be adjustable?
- From: "Scott E. Fahlman" <Fahlman@C.CS.CMU.EDU>
- Date: Wed, 20 May 1987 15:51:00 -0000
- Cc: common-lisp@SAIL.STANFORD.EDU
- In-reply-to: Msg of 20 May 1987 09:37-EDT from David C. Plummer <DCP at QUABBIN.SCRC.Symbolics.COM>
- Sender: FAHLMAN@C.CS.CMU.EDU
Maybe if we could figure out how to express the various types of arrays
using set language we wouldn't accidentally invert phrases. For
example, I think everybody agrees that simple is a subset of
(intersect not-adjustable not-fill-pointer not-displaced)
That's the >only< thing that phrase says. It can't be inverted,
conversed, contra-positived, or anything to say that simple arrays are
not adjustable. The contra-positive (the only thing provably true) is
that the UNION of adjustable, fill-pointered or displaced arrays is a
subset of non-simple arrays.
Gee, it's been a while since I hacked formal logic in any serious way,
but it seems to be true that if X is a subset of the intersection of A,
B, C, and D, then X is (provably) a subset of A. I cheated and used
little pictures instead of contrapositives (my religion forbids the use
of contrapositives, even among consenting adults), but I think it's
still true. Maybe I should go audit a logic course and see what I'm