Definition. Structural quality and good contributor classes [ftip-00MV]
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    Fix a development law and recipient interaction protocol \(\Pi \) before final evaluation. For development input \(D\) and resulting contribution transcript \(H_v\), choose an independently specified structural predicate \(S(D,H_v)\). Define

    \[q_v=\Pr _{\Pi ,v}\bigl (S(D,H_v)\bigr ).\]

    A possible property is a sound reduction to a declared tractable class with bounded translation and certificate-expansion costs. A reusable invariant with a proved consequence or a curriculum satisfying a separate learning condition are other possibilities. A fallible analogy may require charged recipient completion before the property holds. The predicate is not simply that the final score improved; soundness, scope and checking costs require their own arguments. Quality is relative to this task, protocol and budget, not a universal ranking of minds.

    For \(0<q_0\leq 1\), the restricted class

    \[\mathcal G(q_0)=\{v\in \mathfrak V:q_v\geq q_0\}\]

    is legitimate. An existence theorem about a member of this class need not help every contributor outside it. Nonemptiness remains a separate obligation; choosing sources on final test outcomes does not establish pre-evaluation availability. Recruitment and screening costs are necessary when claiming an affordable procedure to find a good contributor, but mere existence does not require a population recruitment theorem.

    To discuss a median, additionally declare a population law \(\mu \) on admissible contributors with measurable quality \(v\mapsto q_v\). Let \(q_{50}\) satisfy \(\mu (q_v\leq q_{50})\geq \frac 12\) and \(\mu (q_v\geq q_{50})\geq \frac 12\). Then define

    \[\mathcal G_\mu (q_0)=\{v:q_v\geq \max (q_0,q_{50})\}.\]

    If \(q_0\leq q_{50}\), this class has at least half the population mass. If \(q_0>q_{50}\), even nonemptiness needs evidence. The median can be zero, so belonging to the upper half alone does not guarantee useful assistance. There is no default uniform law over all possible contributors, and an unattained quality supremum need not have a best contributor.