Who was the first to use the "does not exist" sign ∄? I'm aware that Giuseppe Peano originated serifed ∃ and, moreover that Whitehead and Russell repurposed Peano's serifed ∃; I'm also aware that Gerhard Gentzen introduced the ∃ sans serif (and used it like Russell and Whitehead rather than like Peano). Yet, I cannot find who was the first to use ∄ as ~∃ to mean "there does not exist". Any idea? Thank you.