A × (low × ... × high) [P]describes a quantity that does not change while the process executes. Example:
5 × (3 × 4 × 5 × 6) = 1800
(5 × 3) × (4 × 5 × 6) = 1800
(5 × 3 × 4) × (5 × 6) = 1800
.
. (etc.)
.
A quantity such as P is called an invariant.
Invariants are important to specify for iterative procedures because: