[ Course Documents ] : [ Semantics ]

Previous Contents Next Keyword Index

Loop Invariant Characteristics

I must meet the following conditions:

1. P => I (the loop invariant must be true initially)

2. {I} B {I} (evaluation of the Boolean must not change the validity of I)

3. {I and B} S {I} (I is not changed by executing the body of the loop)

4. (I and (not B)) => Q (if I is true and B is false, Q is implied)

5. The loop terminates (can be difficult to prove)