triple line equals symbol I keep seeing this symbol $\equiv$ in Mathematical Analysis -1, Zorich. What does it mean?
For example: in page 180 we have,

Some other pages it occurs in: 117, 139.

In this case it means "identically equal" and is a shortcut for saying that a function is defined or that some identity holds for all function values, in contrast to $f(x)=x$ which could also mean a fixed-point equation (that is, $f$ is given and one looks for specific $x$).
