# ExpirySettle

> Gives a pool a maturity, and makes moving its price monotonically more expensive as that maturity approaches, so the settlement price is dearest to manipulate exactly when manipulating it would pay most.

A production Uniswap v4 hook. Source: https://github.com/nirholas/expiry-settle. Part of the HookForge catalogue: https://hookforge.pages.dev

## How it works
Any dated instrument that settles against a market price has the same problem at the end of its life. The payoff of pushing the price around is largest in the final minutes, because there is no time left for anybody to push it back, and the cost of pushing it is unchanged from any other moment. Traditional markets answer this with a settlement window: the official price is an average over the closing period rather than a single print, which makes a manipulator pay for the whole window instead of one instant. A pool cannot average its own price without an oracle, but it can do something a traditional venue cannot: change what moving the price costs. As maturity approaches, this hook ramps the fee from `baseFee` up to `settlementFee` across the last `windowSeconds`, on a curve that is quadratic rather than linear so the final moments are much more expensive than the early part of the window:   fee(t) = baseFee + (settlementFee - baseFee) * elapsed^2 / windowSeconds^2 A manipulator who wants to move the settlement print has to choose between acting early, where the fee is low but there is time for somebody to trade against them, and acting late, where nobody can respond but every basis point of the move costs several times more. The fee is paid to the liquidity that has to absorb the move, which is the party bearing the cost. At maturity the pool stops trading. Swaps revert, so the price cannot move again, and `settlementPrice` is simply the pool's final tick. Liquidity may always be removed, including after maturity, because a matured pool that cannot be exited is a trap rather than an instrument. Adding liquidity after maturity reverts: there is nothing left to provide liquidity for, and permitting it would only let somebody strand funds. The hook holds nothing, takes nothing for itself, and has no privileged role. The maturity is fixed before the pool exists and cannot be moved by anyone, which is the property that makes the instrument datable at all.

## Prior art
Dated AMMs exist (YieldSpace and Pendle-style curves converge to par at maturity), and hooks that halt trading on a schedule exist. Settlement-window design is standard in traditional derivatives. Making the *cost* of moving an AMM's price rise on a convex curve into its own settlement, as the on-chain substitute for a time-averaged settlement price, is the contribution here.

## Where it does not help
It raises the cost of manipulation, it does not prevent it. A manipulator whose payoff exceeds the ramped fee will still pay it, and the right response is to size `settlementFee` against the notional settling on the price rather than against ordinary trading. The hook also cannot know what the pool settles for, so if nothing actually references `settlementPrice`, the ramp is pure cost with no benefit.

## Facts
Slug: expiry-settle
Contract: ExpirySettleHook
Callbacks: beforeSwap, beforeAddLiquidity, afterInitialize
Parameters: maturity (uint64), windowSeconds (uint32), baseFee (uint24), settlementFee (uint24)
Dynamic fee required: yes

## Caveats
- Unaudited.
- A deployment with status "deterministic" is a mined CREATE2 address with no code at it yet. Never present one as live.