BMC vs Unbounded Proof Strategies: Comparison Matrix

Comparison matrix

BMC, induction, and PDR-style engines each expose different bug classes and closure tradeoffs.

+------------------+----------------+----------------+----------------+
| Approach         | Strength       | Weakness       | Best when      |
+------------------+----------------+----------------+----------------+
| BMC-first        | fast bug-find  | depth-limited  | startup and shallow bugs |
| Unbounded-first  | strong guarantee | harder setup   | stable invariants |
| Hybrid staged    | balanced flow  | tool tuning effort | mixed property sets |
| Intent-split     | clear ownership | planning overhead | large regressions |
+------------------+----------------+----------------+----------------+

When to choose each approach

• Choose strategy by requirement criticality and residual-risk tolerance, not by runtime alone.

Interview traps

• Applying one setup strategy to all property classes without intent review.

• Accepting waivers before replaying first divergence with owners.

Formal deep dive

Convergence requires engine strategy, invariant quality, and model realism to move together with measurable progress.

Concept diagram

CONVERGENCE DECISION FLOW

property bucket -> engine strategy -> helper invariants -> convergence audit -> closure

Metric graph

CONVERGENCE BURNDOWN

open hard properties    ███████
inconclusive aging      █████
closed with audit       ████████

Metrics and artifacts to collect

• engine effectiveness by property class

• induction and helper-lemma success ratio

• stalled-property aging dashboard

• runtime vs closure-quality movement

Mini case study

A stalled set closed only after case-splitting by mode and auditing fairness assumptions for realism.

Debug branches

• Bucket properties by structure and intent before tuning.

• Inspect proof core stability, not runtime alone.

• Reject speed gains that reduce legal reachability.

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

BMC vs Unbounded Proof Strategies should be reviewed as a requirement-evidence workflow, not a single status report.

Use Bound depth achieved, k-induction success rate, and ratio of bug-find to full-proof properties. as the monitoring lens and Proof intent matrix mapping each property to BMC depth goals, unbounded targets, and escalation criteria. as closure proof.

Convergence is an engineering loop: classify hard properties, tune engines, strengthen invariants, and audit constraints continuously. Strong teams preserve legal reachability while improving convergence.