A dictionary implemented with two hash tables, T₁ and T₂, and two different hash functions, h₁ and h₂. Each key, k, is either in T₁(h₁(k)) or T₂(h₂(k)). A new key, k, is stored in T₁(h₁(k)). If that location is already occupied by another key, l, the other key is moved to T₂(h₂(l)). Keys are moved back and forth until a key moves to an empty location or a limit is reached. If the limit is reached, new hash functions are chosen, and the tables are rehashed. For tables that are a bit less than half full and with carefully chosen universal hashing functions, performance is good. A key is deleted by removing it from a table.