# Interview — Merkle tree and inclusion proofs

**Q1. What problem does this mechanism solve?**
How can a client verify transaction inclusion without downloading all transactions? Construct a binary Merkle tree and verify a sibling proof from leaf to root.

**Q2. What is the naive failure mode?**
Hashing all transactions on every query is wasteful.

**Q3. Is this enough for a secure public blockchain?**
No. This lab isolates one mechanism; production needs cryptographic identities, network rules, adversarial validation, consensus and operational safeguards.

**Q4. What would you test?**
Happy path, malformed input, tampering and disagreement or competing histories where relevant.