Evaluation of interval extension of the power function by graph   decomposition
  The subject of our talk is the correct evaluation of interval extension of the function specified by the expression x^y without any constraints on the values of x and y. The core of our approach is a decomposition of the graph of x^y into a small number of parts which can be transformed into subsets of the graph of x^y for non-negative bases x. Because of this fact, evaluation of interval extension of x^y, without any constraints on x and y, is not much harder than evaluation of interval extension of x^y for non-negative bases x. 
Evgueni Petrov