Draw a state diagram that depicts a simple system that stacks and unstacks a set of Russian Matryoshka dolls. Matryoshka dolls are hollow wooden dolls that can be separated in two parts, revealing a smaller doll inside, which can itself be separated, and so on, until the smallest, solid doll is reached. The system has four states: ready (dolls stacked), ready (dolls unstacked), stacking, and unstacking. Consider the following details of the system operation:

- the system will never stack or unstack dolls out of order; dolls are always placed inside the next largest doll.

- the system can transition between stacking and unstacking mid-sequence; that is, it can switch to stacking again even before all dolls have been unstacked, and vice versa.

You can use an online UML editor ( UMLetino http://www.umlet.com/umletino/umletino.html) for your diagram