> ## Documentation Index
> Fetch the complete documentation index at: https://docs.pfbridge.xyz/llms.txt
> Use this file to discover all available pages before exploring further.

# Merkle Mountain Range

> The append-only deposit ledger — and what changed in v2

Every deposit — a bridger funding an order, a maker locking for one — is
appended as a leaf to that chain's **Merkle Mountain Range (MMR)**, an
append-only tree maintained by the `MerkleManager` contract. The tree's
root commits to every deposit ever made, and the deposit proofs are built
against it. The fundamentals are unchanged from v1
(append-only, Poseidon2-hashed, only the escrow contracts may append) —
this page covers what v2 added.

## Side-bound leaves

A v2 leaf commits to more than the order hash:

```
leaf = poseidon2(field_mod(orderHash), side)
```

The `side` records **which side of the trade this deposit settles** — an
`AdManager` deposit is unlocked on the order side, an `OrderPortal` deposit
on the ad side. Binding the side into the leaf means a proof about one
deposit can never be bent to unlock the wrong side of a trade. This was
part of the T1 hardening set, with a property test guarding it in CI.

## Roots are what you co-sign

Both chains' MMR roots are fields of the
[SettlementAuth](/v2/concepts/co-signing) each party signs. Your signature
therefore authorizes settlement against a *specific, known* state of both
deposit ledgers — if either tree were tampered with afterward, the proofs
wouldn't verify against the roots you signed.

## The relayer's mirror is a rebuildable projection

The relayer keeps a local mirror of each chain's tree to build proofs
quickly — but the mirror is a **projection of on-chain events**, not a
source of truth. It replays the chains' append events and asserts its
root against the on-chain root at every step; wiped, it rebuilds from the
chains alone. Nothing about settlement depends on relayer-held state,
which is what lets anyone run the same code.

## Proofs in seconds

The v2 prover generates an inclusion proof in **seconds** (the v1 flow
took \~90). Same tree, same verifier family — the speed came from
algorithmic and witness-generation changes, and a CI benchmark fails the
build if the bound ever regresses.

## Build on it

The [`proofbridge-mmr`](https://www.npmjs.com/package/proofbridge-mmr)
npm package produces byte-identical outputs to the on-chain contracts —
use it to reconstruct a tree from chain events, generate inclusion proofs
offline, or validate settlement state independently.