First vertical
Connecting MC, A 1M, it is easy to get MC=MA 1, MN is perpendicular to CA 1, and a vertical line comes out.
Second vertical
Taking the midpoint N 1 of CB 1 and connecting BN 1 and NN 1, we can get that NMBN 1 is a parallelogram (NN 1 is parallel and equal to BM), and MN is parallel to BN 1.
At this point, you need sufficient conditions for the three vertical theorems.