On a solution to display non-filled-in quaternionic Julia sets
  During early 1980s, the so-called `escape time' method, developed to display the Julia sets for complex dynamical systems, was exported to quaternions in order to draw analogous pictures in this wider numerical field. Despite of the fine results in the complex plane, where all topological configurations of Julia sets have been successfully displayed, the `escape time' method fails to render properly the non-filled-in variety of quaternionic Julia sets. So their digital visualisation remained an open problem for several years. Both the solution for extending this old method to non-filled-in quaternionic Julia sets and its implementation into a program are explained here. 
Alessandro Rosa