Before revision:  In recent years , powerful compressed indexes have emerged . These are based on Entropy, the Lempel-Ziv factorization, the run-length Burrows-Wheeler Transform (BWT) , context-free grammars and, more recently, string attractors.
After revision:  In recent years , powerful compressed indexes have emerged ; these are based on Entropy, the Lempel-Ziv factorization, the run-length Burrows-Wheeler Transform (BWT) , context-free grammars and, more recently, string attractors.