Mechanistic sub-question
What it producesalso: L5 · drill branch · mechanism drill · tool requirement · model requirement · validation drillThe bottleneck under a discriminating question, classed by what blocks it: cannot measure, cannot isolate, mechanism unclear, or assumptions untested.
Cannot measure it becomes a tool requirement; cannot isolate it becomes a model requirement; mechanism unclear becomes a mechanism drill; assumptions untested becomes a validation drill. Each branch ends in leaf experiments.