Constant product
The AMM rule x × y = k: a pool's two reserves must always multiply to the same constant, so the price is their ratio.
Under the constant-product rule, buying one token from the pool removes it from reserve x and adds the other to reserve y, and the price moves so that x × y is unchanged. The result is that the price paid rises with the size of the trade relative to the pool — a trade of 10% of a reserve costs roughly 10% more than the quoted price. It is the simplest AMM design and still the most widespread.