$u_1$,$u_2$为平面上调和函数,如果对任意的$r>0$,满足$\underset{\left| z \right|=r}{\mathrm{sup}}u_1\left( z \right) =\underset{\left| z \right|=r}{\mathrm{sup}}u_2\left( z \right)...
A biased coin is tossed $N$ times, where $N$ is a random variable with finite mean. Show that if the numbers of heads and tails are independent, then $N$ is Poisson.