## 2.1 The bank — 2.4 Timing of the game

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---

### Overview of actors and incentives
- Financial sector represented by a single bank managed by its owners (owners are residual claimants and not part of the public).
- Funding: deposits of size 1, entirely costless government-insured deposits (no interest, never called).
- Bank choices:
  - Initial asset risk profile  ∈ [0;1].
  - If insolvent, whether to engage in a gamble for resurrection.
- Bank owners obtain full upside of positive bank returns and none of the downside when insolvent (limited liability); bank profits do not enter public welfare.
- Public bears expected cost of insolvency via lump-sum taxes funding deposit insurance.

### Bank’s risk profile — setup and tradeoffs
- Deposit base size: 1.
- Net return on bank assets r ∼ Uniform(mean , half-width w) with support [ w, +w].
  - Example:  = 0:02 and w = 0:05 imply r ranges from  3% to +7%.
- Dependence on risk profile :
  - () = m  (equation (1))
  - w() =  (equation (2))
  -  ∈ [0;1] (equation (3))
- Parameter restrictions:
  -  >  > 0 (4)
  -  +  < 1/2 (5)
  -  +  > m > 0 (6)
- Limited liability implies bank behaves like a call option owner: trades off higher variance (w increases with ) against lower mean ( decreases with ).
- Bank expected profit with limited liability:
  - E[] = E[max{r;0}] =  + w ∫_0^{+w} r f(r) dr (equation (7))
  - Uniform density: f(r) = 1/(2) (8)
- Closed-form and corner solutions:
  - Lemma 1: bank chooses  = 1 if m < m̄;  = 0 otherwise (equation (9))
  - Threshold m̄ =  +  2 sqrt() (equation (10))
  - Consequently model focuses on binary choice between good project ( = 0) and bad project ( = 1); bad project has lower mean and greater exploitation of safety net.

### Gambling for resurrection — mechanism and effect
- Gamble represents zombie lending: reinvestment in failed project with negative expected return.
- Gamble parameters:
  - Success probability g ∈ (0; 1/2]; success raises net return by ( + ) and suffices to bring bank back to positive profit; failure reduces net return by ( + ).
  - Expected return of gamble is negative because g ≤ 1/2.
- Bank objective when gamble allowed:
  - E[] = E[r | r > 0] + E[g (r +  + ) | r < 0] (equation (11))
- An insolvent bank always chooses to engage in the gamble.
- Availability of gamble increases ex ante incentive to choose bad project:
  - Lemma 2: With gamble option, bank chooses  = 1 if m < m_b and  = 0 otherwise (equation (12))
  - m_b =  +  2 sqrt( (1 g) + 1/4 (+)^2 g^2/(1 g)) (equation (13))
  - m_b > m̄ (gamble raises threshold favoring bad project).

### Interaction with the public and information frictions
- Public imperfectly informed; visible variable is realized bank solvency r while bank active.
- Public receives a signal with revelation probability  ∈ (0;1):
  - With probability  the public learns true r while bank remains active.
  - If bank closed (deposit insurance paid), public always learns r.
  - Limits:  → 1 implies perfectly informed public;  → 0 implies public in the dark while bank open.
- If public learns bank is insolvent, it imposes punitive cost x > 0 on the government (electoral loss, demonstrations).
- Expected public cost when no gamble: E[min{r;0}].
- When gamble exists, expected loss to public becomes E[(1 g)(r  ) | r < 0].
- Public’s reaction function is known and anticipated by bank and government.

### Government: objectives, time inconsistency, and policy tool
- Single policymaker represents public interests; government loss function: E[min{Bank returns;0}   x] (text indicates E[minfBank returns;0g]   x), with x measuring sensitivity to public punishment.
- Define x(1 ) as "the extent to which the government is subject to pressure from a poorly informed public".
- Binary regulatory tool l:
  - l = fAllowg: historical cost accounting (allows gambles).
  - l = fForbidg: mark-to-market accounting (forbids gambles by insolvent bank).
- Mark-to-market forces insolvent (r < 0) bank to recognize losses and shut down (prevents gambles); historical cost can veil insolvency and allow gambles.
- Timing and time inconsistency:
  - Government legislates initially before bank chooses .
  - With probability  ∈ (0;1) the government has a second decision stage after r is realized; with probability 1  this stage does not exist.
  -  parameterizes agility/time consistency of legislation: high  = agile legislation but greater time inconsistency;  → 1 makes initial legislation moot;  → 0 initial decision binding.
  - Once r < 0 realizes, the government has incentive to allow gambles to avoid public imposition of x; ex ante regulation against gambles can be undermined if government can change policy later.
- Regulatory tradeoffs:
  - Forbidding gambles ex ante reduces bank incentive to choose bad project but cannot directly target .
  - An ideal tool targets initial risk choice  (discussed in Section 5 extension); model focuses on l as imperfect realistic instrument.

### Game timing (seven stages)
- Stage 1: Government determines l.
- Stage 2: Bank chooses .
- Stage 3: r is drawn.
  - If r > 0: game ends with payoffs r (bank), 0 (public), 0 (government).
  - If r < 0: game continues.
- Stage 4: With probability  this stage occurs and government can again determine l.
- Stage 5: If l = fForbidg, bank shuts down, public repaid deposits, government deposit insurance covers shortfall, public imposes x on government. If l = fAllowg, game continues.
- Stage 6: With probability  the public learns r < 0 and imposes x on government.
- Stage 7: Bank gambles. With probability g gamble succeeds, payoffs are (r +  + ) (bank), 0 (public), government payoff either 0 or  x depending on Stage 6. If gamble fails, payoffs are 0 (bank), (r      ) (public), (r         x) (government).

### Solution approach
- Solve by backward induction: Stage 4, Stage 2, Stage 1 decision nodes analyzed in sequence.

### Key lemmas and conditions (baseline)
- Lemma 3 (government at Stage 4):
  - Government sets l = fForbidg iff
    x(1   ) < r + ( + ) (1   g) / g  (equation (14)).
  - Implication: Government forbids gambles when x(1   ) is smaller than a positive threshold. For x ! 0 government always forbids gambles at Stage 4. For  ! 1 government’s incentive to forbear disappears.
- Lemma 4 (bank’s Stage 2 decision given Stage 1 policy):
  - If l = fAllowg at Stage 1, bank sets  = 1 if m < m_A and 0 otherwise (equation (15)).
  - If l = fForbidg at Stage 1, bank sets  = 1 if m < m_F and 0 otherwise (equation (16)).
  - Ordering: m_F < m_A and m_F < m < m_A. Expressions for m_A and m_F appear in (31) and (33).
- Lemma 5 (government optimal policy at Stage 1):
  - Government chooses l = fAllowg if
    m < m_F  and  x(1   ) > 1/2 m + ( + ) (2   3g) / (2g)  (equation (17));
    otherwise l = fForbidg.
  - Equivalent (18): m < min { m_F ; 3 ( + ) + 2  x(1   )    +   / g }.
  - Interpretation: Government allows gambles when political pressure from poorly informed public is large (x(1   ) large) or when m is too low.

### Proposition 1: non-monotonic interaction of time inconsistency  with policy
- Statement:  interacts non-monotonically with government’s optimal policy. In (17), both @m_F/@ < 0 and @m_F/@ > 0 are possible.
  - @m_F/@ expression given in (38) decomposes into:
    - Term (39): strictly positive — less time consistency reduces tool effect on bank risk-taking.
    - Term (40): strictly negative — increased time inconsistency raises Stage 1 government’s incentive to tie its own hands.
  - Numerical examples:
    - Example 1: = 0:01,= 0:1,g= 0:4,= 0:5,x= 0:1,m= 0:03, at = 0:5 gives @m_F / @ = 0:005 < 0.
    - Example 2: = 0:01,= 0:1,g= 0:4,= 0:75,x= 0:75,m= 0:03, at = 0:5 gives @m_F / @ = 0:047 > 0.
- Intuition:
  -  ! 0 (tool time-consistent) maximizes government influence on bank behavior.
  - Time inconsistency creates conflict between Stage 1 government and Stage 4 future self; net effect on allowance of gambles depends on parameters.

### Extensions: conditioning policy on r and risk caps
- Conditioning policy on bank solvency (l(r)):
  - Government chooses l(r) with l(r) = fAllowg if r ∈ S and fForbidg otherwise (equation (19)).
  - Proposition 2: For r < 0, l(r) = fAllowg iff r < x(1   )   ( + ) (1   g) / g; government plays mixed strategy when r ≥ 0 (equation (20)).
  - Interpretation: Government allows gambles only when bank is sufficiently insolvent; when x(1   ) ! 0 condition never holds and government always forbids gambles.
- Targeting bank risk with a risk cap  (risk-weighted capital requirement shorthand):
  - Government chooses  and l at Stage 1.
  - Frictions:
    - Regulatory arbitrage: with probability  ∈ (0,1) regulation binds ( binds ); with probability (1   ) arbitrage resets  to bank choice.
    - Adjustment cost: if bank chosen  >  and forced down, cost (   ) with  ∈ (0,1).
  - Lemma 6 (bank Stage 2 policy with risk cap):
    -  = 1 if m > b_m_A, 0 otherwise if l = fAllowg;
    -  = 1 if m > b_m_F, 0 otherwise if l = fForbidg (equation (21)).
    - Ordering: b_m_F < b_m_A, b_m_A < m_A, b_m_F < m_F. Limits: b_m_A ! m_A, b_m_F ! m_F as  ! 0. For  ! 1 bad project never chosen.
  - Lemma 7 (government Stage 1 with risk cap):
    - Government optimally sets  = 0, combined with l = fAllowg if m < b_m_F and x(1   ) > 1/2 m + ( + ) (2   3g) / (2g) (equation (22)); otherwise l = fForbidg.
  - Remark:  ! 1 implies  =  = 0 and the socially optimal outcome with payoffs (m; 0; 0).
  - Proposition 3:
    - Proposition 1 remains valid with replacements m_A → b_m_A and m_F → b_m_F.
    - Government uses tools  and l as complements: with risk cap government forbids gambles using l over a larger range of m than without risk cap.

### Policy implications and trade-offs
- Main insight: Interaction of political pressure (public imperfect information) and time consistency of policy tools creates non-monotonic effects on regulatory incentives.
- Key trade-offs:
  - More credible (time-consistent) tools strengthen policymaker ability to constrain bank incentives and can raise incentive to act up front.
  - Less credible tools increase urgency to be tough initially because policymaker anticipates future forbearance by its future self.
- Policy-relevant implications:
  - Granting financial regulators more operational and financial independence can detach incentives from political cycles and reduce muddling through.
  - Improving public information or regulatory transparency (reducing x or increasing ) reduces political pressure and attractiveness of forbearance.
  - Combining direct tools targeting bank risk (risk caps) with regime choice on accounting/forbearance (l) can be complementary and yield closer-to-first-best outcomes, especially when risk cap is effective (high ).
- Overarching message: Time consistency is a double-edged sword — more time-consistent policy tools can either increase or decrease the government’s incentive to protect the public, depending on parameter values and informational frictions.

*Source: wpiea2021001-print-pdf — sections 2.1 and 2.4.*

### 2.1    The bank

### 2.1    The bank

### Overview of actors and incentives
- Financial sector represented by a single bank managed by its owners; owners are residual claimants and are not part of the public.
- Funding side is fixed: entirely costless government-insured deposits (no interest, never called).
- Bank decisions center on asset-side choices: initial asset risk profile () and, if insolvent, whether to engage in a gamble for resurrection.
- Bank profits do not enter public welfare; bank owners obtain the full upside of positive bank returns and none of the downside when insolvent.

### 2.1.1 The bank’s risk profile — setup and tradeoffs
- Deposit base size: 1 (the bank invests deposits of size 1).
- Net return on bank assets, r, is drawn from a uniform distribution with mean  and width w, defined so distribution ranges from  w to +w.
  - Example:  = 0:02 and w = 0:05 imply r ranges from  3% to +7%.
- Both  and w depend on risk profile :
  - () = m  (equation (1))
  - w() =  (equation (2))
  -  ∈ [0;1] (equation (3))
- Parameter restrictions:
  -  >  > 0 (4)
  -  +  < 1/2 (5)
  -  +  > m > 0 (6)
  - Interpretation: as  rises, width increases faster than mean declines ( > ), enabling possible preference for riskier profile;  +  < 1/2 ensures overall gross return nonnegative including gambles;  +  > m > 0 ensures fixed part of mean return is positive but not so large that safest profile is always chosen.
- Due to limited liability, the risk-neutral bank behaves like a call option owner: accrues upside, bounded downside; trades off higher variance (w increases with ) against lower mean ( decreases with ).
- Bank expected profit accounting for limited liability:
  - E[] = E[max{r;0}] =  + w ∫_0^{+w} r f(r) dr (equation (7))
  - Uniform density: f(r) = 1/(2) (8)
- Lemma 1 (closed-form solution for E[]) implies binary optimal choice:
  - Bank chooses  = 1 if m < m̄;  = 0 otherwise (equation (9))
  - Threshold m̄ =  +  2 sqrt() (equation (10))
  - Economic interpretation: low m (less skin-in-the-game) makes variance valuable; high m reduces incentive to increase variance.
- Consequently model focuses on binary choice between good project ( = 0) and bad project ( = 1); bad project is socially detrimental (lower mean, greater exploitation of safety net).

### 2.1.2 Gambling for resurrection — mechanism and effect
- Gambling for resurrection modeled as negative expected return activity (zombie lending): reinvestment in failed project.
- Gamble success probability g ∈ (0; 1/2]; success boosts net return by ( + ) and always suffices to bring bank back to positive profit; failure (probability 1 g) reduces net return by additional ( + ).
- Expected return on the gamble is negative because g ≤ 1/2.
- Bank’s objective when gamble allowed:
  - E[] = E[r | r > 0] + E[g (r +  + ) | r < 0] (equation (11))
- An insolvent bank always chooses to engage in the gamble (only sees upside).
- Availability of gamble makes bank more inclined to choose bad project ex ante; threshold for choosing bad project increases (more values of m lead to bad project).
- Lemma 2: With the gamble option (absent regulation), bank chooses  = 1 if m < m_b and  = 0 otherwise (equation (12)), where
  - m_b =  +  2 sqrt( (1 g) + 1/4 (+)^2 g^2/(1 g)) (equation (13))
  - And m_b > m̄ (i.e., gamble raises threshold favoring bad project).

### Interaction with the public
- Public bears cost of bank insolvency via lump-sum taxes funding deposit insurance.
- Expected cost to public when no gamble option: E[min{r;0}].
- When gamble option exists, expected loss to public becomes (1 g)(r  ) when r < 0, so expected loss is E[(1 g)(r  ) | r < 0].
- Public is imperfectly informed about bank health; only visible (imperfect) variable is realized bank solvency r while bank remains active.
- Public receives a signal with revelation probability  ∈ (0;1): with probability  the public learns true r while bank remains active; if bank closed (deposit insurance paid), public always learns r.
  - Limits:  → 1 implies perfectly informed public;  → 0 implies public completely in the dark while bank open.
- Public prior: bank solvent (r ≥ 0) unless signal or closure reveals otherwise.
- If public learns bank is insolvent, it imposes a punitive cost x > 0 on the government (electoral loss, mass demonstrations, etc.).
- The public’s reaction is modeled as a known reaction function (not explicit optimization); bank and government anticipate this reaction.

### Government: objectives, time inconsistency, and policy tool
- Single policymaker (government) represents public interests; does not value bank owners’ profits.
- Government loss function: E[min{Bank returns;0}   x] (text indicates E[minfBank returns;0g]   x), where x measures sensitivity to public punishment.
  - Define x (1 ) as "the extent to which the government is subject to pressure from a poorly informed public".
- Binary regulatory tool l: legislation about gambles for resurrection.
  - l = fAllowg represents historical cost accounting (allows gambles).
  - l = fForbidg represents mark-to-market accounting (forbids gambles by insolvent bank).
- Mark-to-market forces insolvent (r < 0) bank to recognize losses and shut down (prevents gambles); historical cost accounting can veil insolvency and allow gambles.
- Government legislates initially before bank chooses . With probability  ∈ (0;1) the government has a second decision stage after r is realized (can change policy); with probability 1  this second stage does not exist.
  - Interpretation:  parameterizes agility/time consistency of legislation. High  = agile legislation but greater time inconsistency;  → 1 makes initial legislation moot (government can change later);  → 0 eliminates time inconsistency (initial decision binding).
- Time inconsistency: once r < 0 realizes, government has incentive to allow the bank to gamble to avoid public imposition of x; hence ex ante regulation against gambles is undermined if government can change policy later.
- Regulatory policy tradeoffs:
  - Forbidding gambles ex ante reduces bank incentive to choose bad project but is imperfect because it cannot directly target .
  - An ideal regulatory tool would target the initial risk choice  so the bank would always choose  = 0; such a tool could overcome the model tradeoffs (discussed in an extension in Section 5).
  - The model focuses on mark-to-market vs historical cost accounting as an imperfect but realistic regulatory instrument; alternative imperfect tools discussed in Sections 4 and 5.

*Source: wpiea2021001-print-pdf - 2.1    The bank.*

### 2.4    Timing of the game

### 2.4    Timing of the game

### Game timing and stages
- The game consists of seven stages (Figure 1). Uncertain outcomes are represented by striped boxes.
- Formal stages:
  - Stage 1: The government determines l.
  - Stage 2: The bank chooses .
  - Stage 3: r is drawn. If r > 0: the game ends with payoffs r, 0, 0 for, respectively, the bank, the public and the government. If r < 0: the game continues.
  - Stage 4: With probability  this stage occurs, and the government can once more determine l.
  - Stage 5: If l = fForbidg, then the bank shuts down, the public is repaid its deposits, with the government’s deposit insurance covering the shortfall, while the public imposes x on the government. If l = fAllowg, then the game continues.
  - Stage 6: With probability  the public learns that r < 0, and imposes x on the government.
  - Stage 7: The bank gambles. With probability g the gamble succeeds, then payoffs are (r +  + ), 0 for, respectively, the bank and the public, while the government’s payoff is either 0 or  x, depending on the outcome of Stage 6. If the gamble fails, then payoffs are 0, (r      ), (r         x) for, respectively, the bank, the public and the government.

### Solution approach
- Decision stages solved by backward induction: Stage 4, Stage 2, and Stage 1 are the decision nodes analyzed in sequence.

### Baseline model: key lemmas and conditions
- Lemma 3: If the government gains the opportunity to legislate at Stage 4, its policy is to set l = fForbidg if and only if
  x(1   ) < r + ( + ) (1   g) / g  (equation (14)).
  - Implication: Government forbids gambles when x(1   ) is smaller than a positive threshold. For x ! 0 the government always forbids gambles at Stage 4. For  ! 1 the government’s incentive to forbear disappears.
- Lemma 4: The bank’s Stage 2 decision depends on the government’s Stage 1 decision:
  - If l = fAllowg at Stage 1, then bank sets  = 1 if m < m_A and 0 otherwise (equation (15)).
  - If l = fForbidg at Stage 1, then bank sets  = 1 if m < m_F and 0 otherwise (equation (16)).
  - m_F < m_A and m_F < m < m_A. Expressions for m_A and m_F appear in (31) and (33).
- Lemma 5: At Stage 1, the government’s optimal policy is l = fAllowg if
  m < m_F  and  x(1   ) > 1/2 m + ( + ) (2   3g) / (2g)  (equation (17));
  otherwise l = fForbidg.
  - Equivalent expression (18): m < min { m_F ; 3 ( + ) + 2  x(1   )    +   / g }.
  - Interpretation: Government allows gambles when political pressure from a poorly informed public is large (x(1   ) large) or when m is too low (bank has little skin in the game). Thus worst bank incentives to risk coincide with strongest government incentives to allow gambles.

### Proposition 1: time inconsistency interacts non-monotonically with policy
- Statement: The time inconsistency of the government’s tool, , interacts non-monotonically with the government’s optimal policy. In (17), both @m_F/@ < 0 and @m_F/@ > 0 are possible.
  - The expression for @m_F/@ (shown in (38)) splits into:
    - Term (39): strictly positive — a less time consistent tool has less effect on the bank’s risk-taking incentives.
    - Term (40): strictly negative — increased time inconsistency raises the Stage 1 government’s incentive to tie its own hands.
  - Numerical analysis shows either effect can dominate depending on parameters.
- Intuition and implications:
  - When  ! 0 (tool perfectly time-consistent), government influence on bank behavior is maximized; the government can commit to forbidding or allowing gambles.
  - Time inconsistency creates a conflict between the Stage 1 government and its future self (Stage 4). The possibility of a more lenient future government can make the Stage 1 government more or less inclined to forbid gambles.
  - Net result: The range of m for which the government allows gambles can either expand or contract when  increases. More time consistent tools are not universally welfare-improving; time consistency can "backfire" under some parameter values.

### Extension: conditioning policy on bank solvency
- Setup:
  - Government chooses a policy mapping l(r) with l(r) = fAllowg if r ∈ S and fForbidg if r ∉ S (equation (19)). Government maximizes expected payoff over choice of S.
  - Stage 1 becomes choosing l(r); Stage 4 is cut; stages reindexed accordingly.
  - To prevent public inference of solvency from observed policy, government can play mixed strategies over ranges of r where indifferent.
- Proposition 2: When government conditions legislation on future bank returns, its optimal policy:
  - If r < 0, set l(r) = fAllowg if r < x(1   )   ( + ) (1   g) / g, and fForbidg otherwise (equation (20)).
  - Government plays a mixed strategy when r ≥ 0.
- Interpretation:
  - Government allows gambles only when the bank is sufficiently insolvent.
  - When x(1   ) ! 0 (public perfectly informed  ! 1 or x ! 0), condition in (20) never holds and government always forbids gambles.
  - Greater insolvency (more negative r) increases the upside up to 0 that partially accrues to the public and government, making forbearance more attractive under political pressure.

### Extension: targeting the bank’s risk profile with a risk cap
- New policy instrument: risk cap  (risk-weighted capital requirement shorthand). Timing modified so government chooses  and l at Stage 1.
- Two frictions:
  - Regulatory arbitrage: with probability  ∈ (0,1) the regulation successfully binds bank risk ( binds ); with probability (1   ) arbitrage succeeds and  is reset to bank choice.
  - Adjustment cost: if bank chosen  >  and subsequently forced down, cost is (   ) with  ∈ (0,1).
- Revised timing (Stages 1–8) and payoffs include adjustment costs (   ) where applicable.
- Lemma 6: Bank’s Stage 2 optimal policy:
  -  = 1 if m > b_m_A, 0 otherwise if l = fAllowg;
  -  = 1 if m > b_m_F, 0 otherwise if l = fForbidg (equation (21)).
  - Ordering: b_m_F < b_m_A, b_m_A < m_A, b_m_F < m_F. Limits: b_m_A ! m_A, b_m_F ! m_F as  ! 0. For  ! 1 bad project never chosen.
- Lemma 7: At Stage 1, government optimally sets  = 0, combined with l = fAllowg if m < b_m_F and x(1   ) > 1/2 m + ( + ) (2   3g) / (2g) (equation (22)); otherwise l = fForbidg.
- Remark 1:  ! 1 implies  =  = 0 and the socially optimal outcome with payoffs (m; 0; 0) for, respectively, the bank, the public and the government.
- Proposition 3:
  - Proposition 1 remains valid in this extension: both @b_m_F/@ < 0 and @b_m_F/@ > 0 are possible.
  - Government uses tools  and l as complements rather than substitutes: with the risk cap the government forbids gambles using l over a larger range of m than without the risk cap.
- Intuition:
  - A more binding risk cap reduces frequency of bank failure and thereby reduces Stage 1 government’s incentive to tolerate future gambles to hide insolvency. Hence government becomes more inclined to forbid gambles (mark-to-market) when it has an effective risk cap.

### Conclusion: policy implications and trade-offs
- Main insight: Interaction of political pressure (public’s imperfect information) and time consistency of policy tools creates non-monotonic effects on regulatory incentives.
- Key trade-offs:
  - A more credible tool strengthens the policy maker’s ability to constrain bank incentives and can raise the incentive to act up front.
  - A less credible tool increases the urgency to be tough initially because the policy maker anticipates future forbearance by its future self.
- Policy-relevant implications:
  - Granting financial regulators more operational and financial independence can detach their incentives from political cycles and reduce muddling through.
  - Improving public information or regulatory transparency (reducing x or increasing ) reduces political pressure and the attractiveness of forbearance.
  - Combining direct tools targeting bank risk (risk caps) with regime choice on accounting/forbearance (l) can be complementary and yield closer-to-first-best outcomes, especially when the risk cap is effective (high ).
- Overarching message: Time consistency is a double-edged sword — more time-consistent policy tools can either increase or decrease the government’s incentive to protect the public, depending on parameter values and informational frictions.

*Source: 2.4 Timing of the game — wpiea2021001-print-pdf*

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### wpiea2021001-print-pdf - References

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### Appendix: Proofs — key derivations and results
- Derivation for E[]:
  - From (1), (2), and (8), solving (7) gives
    - E[] = (m+ ( )) 2 4 (equation (23))
  - Convexity: @2 E[] / @2 > 0 for parameter values allowed by (4)-(6); corners are optimal so bank chooses either = 0 or = 1.
  - Expected return when = 0 is m; when = 1 it is (m+ ) 2 4. Equation for m:
    - m = (m+ ) 2 4 (equation (24)), giving solution in (10) and a second excluded solution m = ++ 2 p .

- Lemma 2 (bank optimization with distributional cutoff):
  - Bank’s optimization in (25); expected profit in (26):
    - E[] = m if = 0
    - E[] = (m+ ) 2  g(m  ) 2 +2g(+)(+ m) 4 if = 1
  - Optimal solution: = 1 when m < m (m given by (13)), and = 0 when m > m; m > m found numerically from parameter constraints.

- Lemma 3 (government decision at Stage 4):
  - Government expected payoff when l=fAllowg:
    - (1 g) (r (+) x) +g(0 x (1 ) (0)) = (1 g) (r  ) x(1 g+g) (equation (27))
  - When l=fForbidg government payoff is r x (equation (28)).
  - Government forbids the gamble when inequality in (29) holds, solved to (14).

- Lemma 4 (bank policy thresholds with legislative action l):
  - Bank solves maximization in (30); integrals given f(r) from (8).
  - Thresholds:
    - When l=fAllowg: bank chooses = 1 if m < m_A and = 0 if m > m_A, where
      - m_A = +  q A  2 g 1 g (equation (31))
      - A expression given in (32).
    - When l=fForbidg: bank chooses = 1 if m < m_F and = 0 if m > m_F, where
      - m_F = +  q F  2 g 1 g (equation (33))
      - F expression given in (34).
  - Ordering: m < m_F < m_A < m.

- Lemma 5 (government Stage 1 payoff structure and condition for l=fAllowg dominance):
  - Payoff matrix depends on m relative to m_A and m_F; condition (35) simplifies to
    - x(1 ) > 1 2 m + (+) (2 3g) 2g (equation (36))
  - Also written as
    - m < 3 (+) + 2  x(1 )  + g (equation (37)); combined with m < m_F gives condition in (18).

- Proposition 1 (comparative statics of m_F with respect to):
  - @m_F / @ expression given in (38), decomposed into positive term (39) and negative term (40).
  - Numerical examples demonstrating @m_F / @ can be negative or positive:
    - Example 1: = 0:01,= 0:1,g= 0:4,= 0:5,x= 0:1,m= 0:03, at = 0:5 gives @m_F / @ = 0:005 < 0.
    - Example 2: = 0:01,= 0:1,g= 0:4,= 0:75,x= 0:75,m= 0:03, at = 0:5 gives @m_F / @ = 0:047 > 0.

- Proposition 2 (government indifference and mixed strategy):
  - Government expected payoff conditional on r is (27) for r ∈ S and (28) for r ∈ 2S; solving r x < (1 g) (r  ) x(1 g+g) gives expression in (20).
  - Government uses a mixed strategy over policy for r ≥ 0 with weights satisfying E[r | l=fAllowg] ≥ 0 and E[r | l=fForbidg] ≥ 0.

- Lemma 6 (effect of arbitrage failure probability  on bank thresholds):
  - With term (m ) added, convexity preserved; bank still chooses between = 0 and 1.
  - Modified optimization in (41) implies b m_A < m_A and b m_F < m_F.
  - Limits:
    - b m_A → m_A and b m_F → m_F as  → 0.
    - As  → 1, bank always chooses = 0.

- Lemma 7 (government choice of risk cap  at Stage 1 under binding conditions):
  - When  not binding government indifferent; when binding, government chooses  = 0.
  - For legislative choice l, steps mirror Lemma 5; when bank arbitrage fails and  binds, gambles cannot occur and l is irrelevant.

- Proposition 3 (effects of arbitrage constraint on earlier results):
  - Proposition 1 remains valid with replacements m_A → b m_A and m_F → b m_F.
  - Since b m_F < m_F, government chooses l=fAllowg for a smaller subset of m > 0 and l=fForbidg for a larger subset compared to baseline (Lemma 7 vs Lemma 5).

*Appendix: proofs reference equations and thresholds as presented in the source PDF.*

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_Source: https://www.imf.org/-/media/files/publications/wp/2021/english/wpiea2021001-print-pdf.pdf_
