A double-lined upward arrow symbol serving as both a relation and delimiter in logic and set theory.
Examples
Logical equivalence in propositional logic
p \Uparrow q \text{ means 'neither p nor q'}
Double arrow delimiter in matrix notation
\left\Uparrow \begin{matrix} a & b \\ c & d \end{matrix} \right\Uparrow
Multiple implications in logical statements
A \Rightarrow B \Uparrow C \Rightarrow D