Derivation of delta exponential T=isolated points

For $t>s$, find $e_p$ by computing $$\begin{array}{ll} e_p(t,s) &= \exp \left( \displaystyle\int_s^t \dfrac{1}{\mu(\tau)} \log(1+\mu(\tau)p(\tau)) \Delta \tau \right) \\ &= \exp \left( \displaystyle\sum_{k=\pi(s)+1}^{\pi(t)} \log(1+\mu(t_k)p(t_k) \right) \\ &= \displaystyle\prod_{k=\pi(s)+1}^{\pi(t)} 1+\mu(t_k)p(t_k). \end{array}$$