A dictionary implemented with two hash tables of equal size, T₁ and T₂, and two different hash functions, h₁ and h₂. A new key is put in table 2 only if there are fewer (colliding) keys at T₂(h₂(key)) than at T₁(h₁(key)), otherwise it is put in table 1. With n keys and two tables of size n/2, the most collisions is 0.69... log₂ ln n + O(1) with high probability.