How spin works?
. Simulation
Spin can work on the Promela description by performing a random simulation
. Verification
1) Spin can also generate a C program, which performs an exhaustive search in
    the whole state space to verify whether the design is error-free.
2) Very large verification problem is attacked by ‘bit-state-storage’ technique,
    also known as supertrace, which takes a divide-and-conquer like strategy
    with little side effects.