A.20:1 - Problem frame

An E.18 transformation-flow structure may place a transformation beside signatures, mechanism descriptions, work-planning material, Work, checks, and retargeting material. Those neighboring values do not all have the same internal constraints.

A.20 addresses a narrower question: one identified subject is tested against one identified constraint under stated assumptions and case facts. The result may later be used by a gate or assurance argument, but it is not itself a gate decision or policy consequence.