The chief difficulty here is that almost no one agrees on notation.

Although it was invented in the 1880's by CS Pierce, still today there is a disagreement.

Here is the way I learned it from C.I. Copi. He called ITStroke and dagger.

$\begin{array}{*{20}{c}}P&{}&Q&{}&{}&{P|Q}\\\hline T&{}&T&{}&{}&F\\T&{}&F&{}&{}&T\\F&{}&T&{}&{}&T\\F& {}&F&{}&{}&T\end{array}$and$\begin{array}{*{20}{c}}P&{}&Q&{}&{}&{P \downarrow q} \\ \hline T&{}&T&{}&{}&F\\T&{}&F&{}&{}&F\\F&{}&T&{}&{}&F\\F& {}&F&{}&{}&T\end{array}$

Willard Quine (the greatest American logician of the 20th century) calls it alternative denial.