I just found out that the normals are o.k. The problem is starting at 90 degrees, the left layer sticks out of

the right layer. This is clearly shown on attached figs when I increased the angle of diagonal fold. This seems

an intrinsic problem of simulating paper folding. Only way to avoid this problem is to give a constraint of not

allowing the left layer passing through the right layer. Does Maya has this kind

of feature?