  The considerable effort of writing requirements is only worthwhile if the
result meets two conditions: the requirements reflect stakeholders' needs, and
the implementation satisfies them. In usual approaches, the use of different
notations for requirements (often natural language) and implementations (a
programming language) makes both conditions elusive. AutoReq, presented in this
article, takes a different approach to both the writing of requirements and
their verification. Applying the approach to a well-documented example, a
landing gear system, allowed for a mechanical proof of consistency and
uncovered an error in a published discussion of the problem.
