21.10. You have been assigned to a software team that is developing software, called MemoryDoubler, that provides greater apparent memory for a PC than physical memory. This is accomplished by identifying, collecting, and reassigning blocks of memory that have been assigned to an existing application but are not being used. The unused blocks are reassigned to applications that require additional memory. Making appropriate assumptions and using natural language, define

a. The data invariant.

b. The state.

c. The operations that are likely.