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Re: no empty (zero) string predicate in Elisp

From: Marcin Borkowski
Subject: Re: no empty (zero) string predicate in Elisp
Date: Sun, 26 Apr 2015 22:11:50 +0200

On 2015-04-26, at 21:06, Emanuel Berg <address@hidden> wrote:

> Marcin Borkowski <address@hidden> writes:
>>> "Predicate" is a word from the grammars of human
>>> languages, but I don't know its exact meaning,
>>> neither there or in programming languages (until
>>> now as for programming).
>> AFAIK, "predicate" is a word from /logic/, and it
>> means (more or less) a function which consumes one
>> or more arguments of any type and gives back
>> a truth-value.
> Doesn't all functions in logic do that?

First of all: IANAL (here L = logician;-)).  But...

For starters, in propositional calculus (AFAIK, also in first-order
logic) there are no "functions" per se, since there are no /sets/.
Furthermore, in the logic systems usually used by us mathematicians
there are no /types/.  AFAIK, the analogue of "type mismatch" in these
systems is just a plain old "syntax error".

What you probably refer to is the fact that in these simple logic
systems both predicates and logical connectives "generate"
truth-values.  However, there are other possibilities; analogues of
"functions" in these systems are called "terms".


Marcin Borkowski
Faculty of Mathematics and Computer Science
Adam Mickiewicz University

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