Before revision:  Our main contribution is a constant factor approximation algorithm in this setting for ED with memory\tilde O(n^{\delta}) for any  \delta > 0. In addition to this, we present an upper bound of \tilde O  (n) on the memory needed to approximate ED or LCS within a factor 1+ o(1) in our setting .
After revision:  Our main contribution is a constant factor approximation algorithm in this setting for ED with memory\tilde O(n^{\delta}) for any \delta > 0. In addition to this, we present an upper bound of \tilde O (n) on the memory needed to approximate ED or LCS within a factor 1+ \epsilon .