The Dex (decentralized exchange) module contains the central business logic of Duality. Users may interact with this module to provide liquidity and execute trades according to commonly-accepted exchange semantics.
Duality is a "concentrated liquidity exchange", which means that for a given trading pair, it relies on many different constant-sum AMM pools to fill orders. This is in contrast to simpler AMM exchanges (e.g. Uniswap V2, Osmosis), which rely on a single constant-product market maker pool to fill orders. In constant-product pools, LPs must provide liquidity across the infinite range of trading prices, such that most of their LP is not put to work, and such that they risk suffering impermanent loss if the market moves away from the price at which they provided liquidity. The comparative advantage of the constant-sum AMM design is that it allows users who wish to LP to have total control over where they place their liquidity and how much they charge in fees.