Invariants are conditions that hold throughout a computation. Invariants are useful for specifying data structures since there are certain constraints that must always hold for the data structure. Such invariants are called data structure invariants.
Invariants are also useful for loops in the program and hold across all interations of the loop. Such invariants are called loop invariants. An invariant for a function holds both before the function is called and after the function has completed running.
Add the function invariant feature to Speclang. One or more function invariants could be specified at the beginning of specification cases: