Let's talk our way through it.

我们再回过头来看一遍
What's it saying?

定义是什么意思呢
It's saying that ? is evolutionarily stable

策略?是进化稳定的
if against all possible mutations,

如果对于任意突变
so all possible versions of Rahul S',

即对于拉胡尔来说任意可能的突变S‘
the payoff of ? against the subsequently mixed population is bigger

对种群内不同个体的收益
than the payoff of S' against the subsequently mixed population.

大于S'对种群内不同个体的收益
Let's just see why that is so.

我们来看看为什么要这么说
So this on the left is the payoff of ? against a population

左边这部分是?对种群内个体的收益
in which 1 - ε of the population like it is playing ?

其中1-ε的概率下是?对?
and ε of the population is like Rahul,

而ε的概率下是?对拉胡尔这类突变个体
because 1 - ε of the time it meets something like itself,

因为1-ε的概率下是与同学配对