Example in man page for 'core is-installed' doesn't work

The example in the man page always acts like WordPress is not installed.

This works for me (removed the square brakets).

    if ! $(wp core is-installed); then
        echo 'Not installed'
    fi

or maybe…

    $(wp core is-installed)
    if [ $? -ne 0 ]; then
        echo 'Not installed'
    fi