Soft-Soft Body, Soft-Rigid Body Collision Documentation

[Ugras]

Dear all,
In order to understand Bullet Soft Body collision detection, Is there any suggested reading/documentation for soft-soft, soft/rigid body collision detection besides the ones given at the end of Bullet User Manual that are respectively : Real Time Collision Detection, Collision Detection in Interactive 3D Environments and Physics Based Animation?
Regards,
Ugras

PS: I haven't received any reply from another board index, therefore, I'm asking the same question here.