Saddle Point

Worked case · Chapter 6, Leadership and Rules: Inspection · p. 242 · sources checked 9 November 2026

Verifying where controlled chips are

what does a verification rule cost compliant licensees, what does a margin of deterrence cost, and which improvement in the check is worth more?

The network

commits announced rule: review with r_f after a fail, r_c after a passacts where the shipment issignal pass or fail, seen before the review decisionacts review or notLicensing authoritythe inspectorLocation checkfails with probability β if diverted, α if notLicenseedivert or comply; many with different stakes in fact
leader, commits first an object of the game player Model N. A reading of the mapping table, drawn by the site. Hover a node or an arrow; the arrows in words:
  1. Licensing authority → Licensee commits announced rule: review with r_f after a fail, r_c after a pass
  2. Licensee → Location check acts where the shipment is
  3. Location check → Licensing authority signal pass or fail, seen before the review decision
  4. Licensing authority → Licensee acts review or not

The mapping

The six fields of the model card, as the book fills them in for this situation.

FieldIn the case
1 Decision-makersa licensing authority (the inspector, leader) and one licensee that may divert a controlled shipment (the inspectee); many licensees with different stakes in fact
2 Timetwo shipment periods and one licence review (an end-use check or a review of the licence able to uncover a diversion), standing for the authority's scarce review capacity
3 Informationbefore deciding on the first period the authority sees the result of a location check: it fails with probability if the shipment has been diverted and if it is where the licence says; the licensee knows the rule, not the result or the draw
4 Commitmentthe authority announces its rule: review with probability after a failed check and after a passed one
5 PayoffsModel N's: no diversion ; a diversion found by review, followed by revocation and penalties, ; a diversion not found ; a review spent on a compliant shipment leaves the second period unreviewed. Deterrence depends on the licensee's payoffs only through its gain share
6 Strategiesrules ; divert or comply

What the mathematics licenses.

Six statements, each about the model under the card above; the mapping to export licensing is a reconstruction R, and no statement estimates the performance of any real check or rule.

  • The authority's loss is the burden on compliant licensees. Under the optimal announced rule the authority's value is times the probability that a compliant shipment is reviewed (Proposition 6.19 (p. 263)(a)). At the base point the rule reviews of failed checks and no passed ones; a compliant shipment faces review with probability , and the authority's value is . Inside the model, lowering the burden on compliant licensees and improving the authority's value are the same objective; they come apart only through the margin of item (iii) D [Proposition 6.19 (p. 263)(a)].
  • Acting on part of the failed checks is optimal exactly when the check catches enough. The optimal rule reviews only a fraction of failed checks iff ; below that line it must review every failed check and a random fraction of passed ones, as in the rows of Table 6.1 (p. 246) with , (a twenty-first of passes) and . In both regions every review that actually takes place falls on a compliant licensee, because the rule works through the reviews a diverter would face D [Proposition 6.19 (p. 263)(a), Proposition 6.11 (p. 258); Figure 6.3 (p. 233)].
  • Reviewing every failed check buys a margin, at a price. At the base point the rule “review every failed check” carries a burden of , which is times the least burden. In exchange it deters every gain share — here — and deters strictly: a diverter would expect against for compliance. The optimal partial rule deters only gain shares up to and leaves that licensee indifferent; if the authority has misjudged the stakes, or the indifferent licensee diverts, the authority obtains (Section 6.4 (p. 229)). Figure 6.7 (p. 247) prices every intermediate margin: the least burden that deters all gain shares up to . A check with a lower detection rate, , has a higher curve; reviewing all its failed checks deters gain shares only up to , and beyond that point passed checks must be sampled D [Proposition 6.19 (p. 263)(c)].
  • Per unit, false failures cost more than missed diversions — where partial action is optimal. In that region the lever ratio is , whatever the payoffs: at the base point and , a ratio of exactly . For a step of the gain is from a higher detection rate and from a lower false-failure rate. The value also depends on the check only through there, so, between two checks that both lie in that region, halving the false-failure rate is worth exactly as much as doubling the detection rate. Where passed checks must be sampled the ordering reverses, ( at ). The reason for the first ordering is that of Chapter 3's lever ratio (Remark 6.20 (p. 265)): false failures act on the equilibrium path, the detection rate only through the threat. Whether a unit of either rate costs the same to achieve is outside the model D [Proposition 6.19 (p. 263)(a), (b); Table 6.1 (p. 246)].
  • A mandated check is not yet a rule. The bill as introduced mandates a mechanism and a duty to report; in the sections read, it does not prescribe what follows a failed check. In the model the value lies in the pair, check and rule, and the same check supports rules whose burdens differ by the factor of item (iii). A response fixed in advance as “revoke on every failure” is the right-hand end of Figure 6.7 (p. 247), not its optimum; and a rule that relies on certified documents rather than a technical check is a different signal, whose two error rates the certifications themselves do not reveal R.
  • A check the licensee can shape is outside the model. The technical literature describes delay that can be added or removed by the party being checked, and the 2026 indictment alleges replica equipment staged for inspection D [Brass and Aarne 2024, pp. 22–23; U.S. Department of Justice 2026, allegations]. If the diverter can buy a higher probability of passing, is no longer a property of the check but a choice of the inspectee, and the error rates must be derived from a game, as in Chapters 4 and 5; the values above then no longer follow from the check's specification alone R.

Where the mapping breaks.

There are many licensees, with different gain shares, and the authority does not know which it faces; the margin of item (iii) is one answer, a distribution over gain shares (Chapter 8) another. Review capacity is a rate per period, not one review over two periods, and the model's mechanism for the authority's loss (a review spent on a compliant shipment leaves the next one unreviewed) is a stand-in for that rate. A failed check imposes direct costs on a compliant licensee, such as delays, a suspended licence or the cost of proving compliance, which Model N does not price: there a reviewed compliant inspectee is no worse off. A check is repeated, and its results accumulate over time, which turns one signal into a sequence (Chapter 1's experiments). A rule written into regulation is hard to randomise; a fraction of failed checks is implementable only through discretion in selecting cases for review, and discretion is itself a commitment problem. A rule that acts on licences has no hold on chips exported without one, as charged in the 2025 case; a check may still reveal them, but the consequence is then a prosecution, with a different payoff structure. And the error rates can be shaped by the licensee, as item (vi) says.

In the book

The full case runs through six steps: The situation, as documented; The model card; What the mathematics licenses; Where the mapping breaks; What one would have to measure; Sources. The numbers in step 3 are certified in the chapter's engine room, and the sources in step 6 are listed with the day they were read. The site shows steps 3 and 4; the rest is on p. 242 of the book.