若定义在区间$-2013,2013$上的函数$f\left(x\right)$满足：对于任意的$x_1,x_2\in -2013,2013$，都有$f\left(x_1+x_2\right)=f\left(x_1\right)+f\left(x_2\right)-2012$，且$x>0$时，有$f\left(x\right)>2012$，$f\left(x\right)$的最大值、最小值分别为$M,N$，则$M+N$的值为(   )

不等式组$\left\{\begin{array}{c}3x-5<2x\\ \frac{x-1}{2}\le 2x+1\end{array}\right.$的解集是____ ．

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                                                                                                      十五夜望月
                                                                                                           王建
                                                                                        中庭地白树栖鸦，冷露无声湿桂花。
                                                                                        今夜月明人尽望，不知秋思落谁家。