The Gabbay–Pitts “nominal” NEW quantifier (fresh-ness)
иa.φ(a)

The  mathematical meaning to ‘for a fresh name’ introduced in my thesis, introduced in A new approach to abstract syntax with variable binding and the prominent new quantifier of nominal logic.

If you type this into LaTeX…

\usepackage{graphics} %needed for the NEW quantifier
\newcommand\new[0]{\reflectbox{\ensuremath{\mathsf{N}}}} 
%The quantifier itself, a reversed sans-serif N 
%(by analogy with the reversed E of `exists' 
%and the reversed A of `forall') 
\newcommand\New[1]{\new #1.} 
%A macro, as in \New{a}\phi
The $\new$ quantifier

… you get this:


Backwards sans-serif N

This is not a russian letter! It is a reflected sans-serif roman letter, by analogy with ∀ the reflected A of ‘for all’ and ∃ the reflected E of ‘exists’.

I wish I’d thought of this pun but it’s one of Andrew Pitts’s ideas. When we discovered (invented?) the NEW quantifier, he suggested a backwards N notation, and this impressed me very deeply.
Simple and commonsense can also be brilliant — even in computer science. I made a mental note.