I am reading a book on differential topology and the first question in it has me confused.
If $k < l$ we can consider $\mathbb{R}^k$ to be the subset $\{(a_1, \cdots,a_k, 0, \cdots, 0)\}$ in $\mathbb{R}^l$. Show that smooth functions on $\mathbb{R}^k$, considered as a subset of $\mathbb{R}^l$, are the same as usual.
What does it mean same as usual?