symbols/codepoints for necessity and possibility in modal logic

Hi all,

Modal logic uses a "box" and a "diamond" (this is how they're informally
called) as operators (accepting one formula and returning another) to
denote necessity and possibility, resp. Older texts might use the
letters L and M (resp). Which Unicode codepoints do modal box and
diamond correspond to?

According to the charts, it seems like the box is
     ◻ (U+25FB)
(is this definitive?), but what about the diamond? Unlike what one might
glean from the charts, ⟠ (U+27E0) is afaiu /not/ normally used to denote
possibility in the default† sense. Wiki's "List of logic symbols"
article has something to say about this too, but I'm always cautious
about information from there.

Stephan

    † eg in the sense of "λ𝑥 . ¬◻¬𝑥" with ◻ as used in say the axiom
    schema conventionally named *T* in modal logic
Received on Thu Jul 18 2013 - 22:30:04 CDT