In 1995, Nisan and Ta-Shma showed the surprising result that SL is closed under complement, which at the time was believed by many to be false; that is, SL = co-SL. Equivalently, if a problem can be solved by reducing it to a graph and asking if two vertices are in the "same" component, it can also be solved by reducing it to another graph and asking if two vertices are in "different" components. However, Reingold's paper would later make this result redundant.