问题如下：
Under what conditions are conditional expectations and marginal expectations equal?
选项：
解释：
If the two components X1 and X2 are independent, then the conditional expectation of any function of X1 given X2 = x2 is always the same as the marginal expectation of the same function.
That is, E[g(X1)|X2 = x2] = E[g(X1)] for any value x2.
请帮我看一下我的理解是否正确：
step1：如果X1,X2这2个随机变量相互独立，那么P(X1| X2=x2)=P(X1), 即【X=x2时，X1的条件概率】=【X1的非条件概率】
step2：所以E(X1| X2=x2)=E(X1)，即conditional expectation of X1 by given X2=marginal expectation of X1
请问：这样理解对么？
由step1推导出step2？
