On the Algebra of Elementary Embeddings of a Rank into Inself
  Let $j:V_\lambda---> V_\lambda$ be an elementary embedding, with critical point $\kappa$, and let $f(n)$ be the number of critical points of embeddings in the algebra generated by $j$ which lie between $j^n(\kappa)$ and $j^{n+1}(\kappa)$. It is shown that $f(n)$ is finite for all $n$. 
Richard Laver