What are Lehmanʼs Laws and how were they derived?

What are Lehmanʼs Laws and how were they derived?
Answer: Continuing change: A program that is used in a real-world environment must necessarily change, or else become progressively less useful in that environment.

Increasing complexity: As an evolving program changes, its structure tends to become more complex. Extra resources must be devoted to preserving and simplifying the structure.

Large program evolution: Program evolution is a self-regulating process. System attributes such as size, time between releases, and the number of reported errors is approximately invariant for each system release.

Organizational stability: Over a program’s lifetime, its rate of development is approximately constant and independent of the resources devoted to system development.

Conservation of familiarity: Over the lifetime of a system, the incremental change in each release is approximately constant.

Continuing growth: The functionality offered by systems has to continually increase to maintain user satisfaction.

Declining quality: The quality of systems will decline unless they are modified to reflect changes in their operational environment.

Feedback system: Evolution processes incorporate multi-agent, multi-loop feedback systems and you have to treat them as feedback systems to achieve significant product improvement.