⁷ The notation we are describing is the most common, but there is no universal standard. Different writers will sometimes use different symbols to express the same logical concept, either for intuitive clarity, or for more prosaic reasons (like the fact that the ¬key doesn’t appear on a standard keyboard). In many programming languages, the symbol “!” is used for ¬, the symbol “&&” for ∧, and the symbol “||” for ∨.