In the subject of the change of variables via integration of 2-forms on $\mathbb{R}^2$ for a function $\omega=f(x,y) dx \wedge dy$ over $D \subseteq \mathbb{R}^2$, the teacher says that we go from a domain $id(x,y)$ to a domain $(x,y)$. And by what he says, that symbol $id(x,y)$ seems to be called - a point "identity" thing that goes to another point $(x,y)$. Can someone tell me what that "$id(x,y)$" really mean.
Here is the link to the YouTube video and look at it at 3:16 minutes at the "trivial parametrization". Thank you in advance for your patience with a physicist that never saw that abbreviation but who is learning something absolutely fantastic. Mario
It's the identity function on $D$. It's a function $id : D \to D$ defined as $id(x,y) = (x,y)$
He's using it to show how the change of variable works for a trivial case.