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Wrapping Up

You’ve built a working mental model of Aztec’s stack:

  • Private state uses a dual‑tree design (note hash + nullifier) and read=write semantics to keep reads current and unlinkable.
  • Public state lives in the Public Data Tree (indexed Merkle), supporting membership and non‑membership at the head.
  • Wallets prove the private phase via the kernel chain and hand off to the network; the sequencer executes public phases (non‑revertible → setup → app logic → teardown) and settles fees in teardown.
  • dApps query balances via contract methods; wallets/PXE select notes internally. Only contracts read notes.

From here, you can dive deeper where it matters most to you:

  • Private execution and kernels: see Private Kernel and the circuit topology in the protocol specs.
  • Transaction execution and statuses: the AVM public simulator and receipt mapping in aztec‑packages.
  • State trees and proving: Note/Nullifier/Public Data trees in the protocol specs.

🧠 Knowledge Check​

Q1: Why do reads of private mutable values emit a nullifier and re-create the note?​

Details

Solution Non-membership in the nullifier tree must be checked at the head by the sequencer. Emitting the nullifier ties validity to “currentness”, re-creating the note (new randomness) keeps the value available without linkability.

Q2: Which trees are append-only versus indexed, and why?​

Details

Solution Note Hash and Archive trees are append-only (membership with historical roots). Nullifier and Public Data trees are indexed to support efficient non-membership at head.

Q3: Where are transaction fees settled, and what happens on failure?​

Details

Solution Fees are settled in the teardown phase. If teardown reverts, receipt status is teardown_reverted; non-revertible effects remain.

Q4: How should dApps obtain a user’s private balance?​

Details

Solution Through contract methods (e.g. balance_of_private). dApps don’t read raw notes; wallets/PXE select notes internally when building transactions.

Q5: Who checks non-membership and when can historical roots be used?​

Details

Solution Non-membership is checked by the sequencer at the head (indexed trees). Historical roots can be used for membership in append-only trees.