Solution
= Solution
For independent identically distributed nonnegative random variables $\xi_1,\xi_2,\ldots$, define the renewal epochs
$$
S_0=0,
\qquad
S_n=\sum_{i=1}^n\xi_i.
$$
The associated <renewal process> is
$$
\boxed{N(t)=\max\{n:S_n\leq t\}},
$$
the number of renewals by time $t$.