B.5.RC:4.3 - Follow prerequisites backward

Start with an operation that produces the required result. Ask what must be available just before it can be applied. Repeat for any prerequisite not yet supplied.

Keep joint prerequisites together: drawing a segment between two points requires both points. Keep alternative constructions separate: either one complete construction or another may produce an acceptable result. Where several later steps use an intermediate object, retain that shared dependency instead of silently creating several unrelated objects.

Stop tracing a branch when it reaches an available input or an understood subconstruction whose starting inputs are available. The resulting dependency structure may have shared parts and alternatives. Draw it when that helps retain them; the structure does not have to be expressed as a graph.

If tracing returns to a result that it already requires, examine the source. It may describe an iterative construction with a starting value and stopping rule, a simultaneous problem with a separate solving method, or an omitted prerequisite. Recover that method or prerequisite before treating the circular description as executable steps.

A missing operation gives a focused question: “How is this intermediate object obtained under these conditions?” Return to the relevant source passage or specialist with that question. When you propose an operation yourself, treat it as a contribution to the construction and establish the conditions for using it.