Bounded Proof Signoff: What a Depth Actually Proves: Interview Drills

Interview drills

Interview Drills for Bounded Proof Signoff: What a Depth Actually Proves is anchored on non-vacuous closure rate, counterexample turnaround, and residual-risk trend by requirement class. Convert outcomes into assumption-aware, evidence-backed actions.

PROMPT
You observe regression in non-vacuous closure rate, counterexample turnaround, and residual-risk trend by requirement class for Bounded Proof Signoff: What a Depth Actually Proves. Explain root cause and signoff decision.

STRONG ANSWER
1. Defines requirement context and first divergence.
2. Explains mechanism: Bounded model checking proves properties for executions up to a finite depth, which is valuable but fundamentally different from unbounded inductive closure.
3. Requests proving artifact: closure packet for Bounded Proof Signoff: What a Depth Actually Proves: assumptions audit, proof status matrix, and replay-ready divergence trace
4. Proposes bounded fix + owner + rollback-safe validation.

WEAK ANSWER
Gives generic formal advice without model boundaries, proof quality, or ownership.

Formal deep dive

Signoff quality is requirement-centric and must integrate proof status, reachability, bounded limits, and waiver governance.

Concept diagram

FORMAL SIGNOFF PYRAMID

requirements -> properties and covers -> quality metrics -> waiver governance -> release decision

Metric graph

SIGNOFF CONFIDENCE TREND

fully proven critical    ███████
bounded-only critical    ████
unexplained cover gaps   ███

Metrics and artifacts to collect

• requirement-to-proof closure map

• critical cover reachability and gap aging

• bounded-only risk register

• waiver debt with owner and expiry

Mini case study

A release review blocked signoff until bounded-only properties were paired with explicit residual-risk and replay plans.

Debug branches

• Separate status color from proof quality dimensions.

• Treat unreachable critical covers as signoff blockers.

• Document bounded-horizon rationale with architecture limits.

Senior review question

Ask: which requirement intent is proven, under which assumptions, and what residual risk remains?

Key takeaways

• Tie each proof claim to assumption boundaries and reachability evidence.

• Prefer minimal reversible fixes and preserve legal behavior visibility.

Common pitfalls

• Treating runtime reduction as proof-quality improvement without audits.

• Declaring closure while critical covers remain unreachable.

• Using broad waivers instead of first-divergence root-cause ownership.

Principal formal review addendum

Bounded Proof Signoff: What a Depth Actually Proves should be reviewed as a requirement-evidence workflow, not a single status report.

Use non-vacuous closure rate, counterexample turnaround time, and requirement-level residual risk trend as the monitoring lens and formal closure packet: assumptions audit, proof status matrix, counterexample classification, and requirement traceability as closure proof.

Signoff is requirement-centric evidence synthesis, not a single dashboard percentage. Strong teams preserve legal reachability while improving convergence.