Savitch's theorem.
Scott Aaronson at the University of Texas maintains an online "zoo" devoted to classifying these things. The spacing between these collections are both arbitrarily large and possible to calculate according to the Borodin-Trakhtenbrot Gap Theorem. Laszlo Kalmar coined the term ELEMENTARY for one of these sets, which is formed by taking the union of a group of sets that comprise the exponential hierarchy. Two spatial examples of these sets are equivalent according to (*) Savitch's theorem. A specific one of these sets is defined as the group of problems whose solutions are verifiable using a nondeterministic Turing machine in polynomial time. The hardest problems in many of these sets are termed "complete." For 10 points, name these sets used to classify computational complexity, such as P and NP.
Scott Aaronson at the University of Texas maintains an online "zoo" devoted to classifying these things.
computational complexity classes 