Best result
Theorem (Tarjan, 1975): There is an implementation of the Disjoint Set ADT such that the worst case time to perform any sequence of n-1 weighted Unions and m >= n Finds is Theta(m a(m,n))
a(m,n) is the inverse Ackermann function
a(m,n) <= 4 for all n < 22 (17 times)