If we want to express that two numbers $x, y$ are not so far away from each other absolutely we use the absolute value function $|\cdot|$ with $0 < \epsilon \ll 1$:
$$|x-y| < \epsilon$$
which is equivalent with:
$$x > y\quad\wedge\quad x-y < \epsilon$$
or
$$x < y\quad\wedge\quad y-x < \epsilon$$
What's the name (and shorthand) of the function that tells us that two numbers $x, y$ are not so far away from each other relatively:
$$x > y\quad\wedge\quad x/y < 1 + \epsilon$$
or
$$x < y\quad\wedge\quad y/x < 1 + \epsilon$$