Position: Ownership and Fee Accounting

Key takeaway: A V3 position is keyed by keccak256(owner, tickLower, tickUpper) — same owner, same range, same position; there is no LP token in the core. Position.update is a checkpoint-then-accrue machine: it computes fees earned since the last touch as mulDiv(feeGrowthInside - feeGrowthInsideLast, liquidity, Q128), adds them to tokensOwed, and overwrites the checkpoint. Fees never auto-compound — they sit as a tokensOwed debt until collect pays them out. The fee-delta subtraction lives in unchecked (the accumulators are relative and wrap by design, section 4), and tokensOwed += fees may overflow by explicit design decision — Uniswap's own comment: withdraw before you hit type(uint128).max fees. The 'NP' require blocks pokes on empty positions.

What You Are Building

The Position library — the last piece of Part 1's math stack. Two functions: get (the mapping key) and update (liquidity changes plus fee accrual). Provided: FullMath, FixedPoint128, and your LiquidityMath from section 2. Short section, but it's where the fee machinery you built in section 4 finally pays a user.