Finally, Olum and Everett note a theorem proven by Stephen Hawking in a 1992 paper on the Chronology Protection Conjecture, which demonstrated that according to General Relativity it should be impossible to create closed timelike curves in any finite region that satisfies the weak energy condition, meaning that the region contains no exotic matter with negative energy. Mallett's original solution involved a spacetime containing a line source of infinite length, so it did not violate this theorem despite the absence of exotic matter, but Olum and Everett point out that the theorem "would, however, rule out the creation of CTC's in any finite-sized approximation to this spacetime."