On 2024-09-16, Ivan Panchenko via Unicode <[email protected]> wrote: > The white concave-sided diamond (⟡) has the informative alias “never > (modal operator)”. I would have expected it to mean the opposite > because U+25C7 (◇, white diamond) is used for possibility rather than > impossibility. Two sources that support my view:
I can't say, as a sometimes practising modal logician, that I've ever seen this symbol as a distinct grapheme. In particular > https://books.google.com/books?id=41VYDwAAQBAJ&pg=PA211 This is not semantically ⟡ distinct from some other diamond, it's just a diamond that has been designed slightly concave; or if it is actually a distinct character in the font, it's an authorial choice (or error), as it's clear from the text that the author is intending the standard modal diamond, which is used for `possibly' in modal logic and `sometime' in temporal logic. > https://www.mdpi.com/2079-9292/8/10/1163 This paper is the area I used to work in. Here one can see that the diamond is indeed U+27E1, but nonetheless the author is using completely standard notation for LTL, and is, either through the random facilities of their authoring software or deliberate aesthetic choice, using a concave diamond rather than a straight diamond. You should be looking for an author who uses straight and concave diamonds contrastively. I imagine that somebody has, though personally I would consider it a perverse notation to make ⟡ mean `never'!
