What I want to do first is to prevent the flap A crossing the flap B, i.e., the rotation just stop when it touches the flap B even though a larger rotation is given to it.

In other words, I want...

I have a paper folded to make two flaps A and B.

If I rotate the flap A a little more, then It will just pass through the flap B.

I want to make the paper more realistic so that it pushes the...