I am studying the book Introduction to tensor analysis and the calculus of moving surfaces, where the covariant basis is defined as the collection of vectors $\mathbf{Z}_i$ obtained from a position vector $\mathbf{R}(Z)$, by differentiation with respect to each of the coordinates $Z^i$:
$$\mathbf{Z}_i = \frac{\partial\mathbf{R}(Z)}{\partial Z^i}$$
At a subsequent exercise, the question is: "What are the components of the vectors $\mathbf{Z}_i$ with respect to the covariant basis $\mathbf{Z}_j$ ?". The author claims that the answer is a "single symbol" introduced in a previous chapter. The only "single symbol" previously introduced is the Kronecker delta ${\delta^i}_j$. However, in the book the Kronecker delta is defined as:
$${\delta^i}_j = \frac{\partial Z^i}{\partial Z^j}$$
so it involves the components $Z^i$ and $Z^j$ and not the collection of vectors $\mathbf{Z}_i$ and $\mathbf{Z}_j$.
How is the question related to this possible answer then?