A celebrated theorem of Savitch states that NSPACE(S) is contained DSPACE(S^2). In particular, Savitch gave a deterministic algorithm to solve ST-CONNECTIVITY (an NL-complete problem) using O(log^2{n}) space, implying NL is in DSPACE(log^2{n}). While Savitch’s theorem itself has not been improved in the last four decades, studying the space complexity of ... more >>>