4. For the equation $\left(1+m^{2}\right) x^{2}-2 m(1+n) x+m^{2}+n^{2}=$ 0 to have integer roots, find the conditions that integers $m, n$ must satisfy, and determine these two integer roots.
(Answer: $m$ is an integer and $m^{2}=n, x_{1}=x_{2}=m$ )