TITLE: Limits notation
QUESTION [34 upvotes]: I'm wondering what is the difference in the use of
$$\lim\limits_{x \downarrow  a}$$
$$\lim\limits_{x \searrow  a}$$
$$\lim\limits_{x \nearrow  a}$$
$$\lim\limits_{x \uparrow  a}$$
I see them around and I don't know what they really mean. Do the arrows characterize how $x$ tends to $a$?

REPLY [30 votes]: Arturo Magidin:

$x↓a$ means that $x$ is approaching a "from above", in a decreasing manner; it's much like $x→a^+$, "approaching from the right"; same for $x↘a$. $x↑a$ means $x$ approaches a from below, in an increasing manner, much like $x→a^−$.