Variations on implication (fwd)

Lulu of the Lotus-Eaters mertz at gnosis.cx
Thu Feb 13 00:13:38 CET 2003


|> Paul Rubin wrote:
|> > => is the traditional mathematical symbol for boolean implication.
|> > -> looks more to me like some kind of pointer operation.  But either
|> > one is ok with me for this.

Michael Hudson <mwh at python.net> wrote previously:
|In which context?  In my world, => is implication.  It's even
|$\implies$ in LaTeX, I think. -> is often used to denote a map.

FWIW, my math background is primarily in logic, model theory, and set
theory.  In those contexts, there is often a convention of using the
single line "->" for syntactic implication, i.e. predicate logic.  The
double line "=>" is reserved for semantic implication.  So you might
write (in a simple case):

    A -> B
    B -> C
    =>
    A -> C

Or:  given the predicates "A implies B" and "B implies C", you are
authorized to derive the predicate "A implies C" (syllogism).

Yours, Lulu...

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