I was hoping someone might be able to shed some light on the choice of indices for expressing the coaction using Sweedler notation.

For example, in the paper of Andruskiewitsch *About finite-dimensional Hopf algebras*, (see page 3) http://cel.archives-ouvertes.fr/docs/00/37/43/83/PDF/2000Andrusk.pdf, $C$ is a coalgebra, $V$ is a left comodule, and the structure map is expressed as

$$\delta: V \longrightarrow C \otimes V$$ $$\delta(x) = x_{(-1)} \otimes x_{(0)}$$

Can someone explain this choice of indices and how it is meaningful for understanding the coaction? I am working on building an intuition for comodules apart from the fact that they are dual to modules, and understanding this notation would be helpful.

The use of Sweedler notation for the comultiplication is familiar and clear to me:

$$\Delta(x)= x_{(1)} \otimes x_{(2)}$$

but I am unsure of the significance of the $(-1)$ and $(0)$.