Are these equal? $\int^t_0 \exp(t-s) \int^s_0 \exp(s-\tau) f(\tau)d\tau ds$=$\int^t_0 f(\tau)d\tau \int^t _\tau \exp(t-s) \exp(s-\tau) ds$

Question

I had difficulties while reading the paper. I did not know why integral is divided and exp function is moved would you please help me?

$\int^t_0 \exp(t-s) \int^s_0 \exp(s-\tau) f(\tau)d\tau ds$ = $\int^t_0 f(\tau)d\tau \int^t _\tau \exp(t-s) \exp(s-\tau) ds$