We study planar drawings of directed graphs in the L-drawing standard. We provide necessary conditions for the existence of these drawings and show that testing for the existence of a planar L-drawing is an NP-complete problem. Motivated by this result, we focus on upwardplanar L-drawings. We show that directed st-graphs admitting an upward(resp. upward-rightward-) planar L-drawing are exactly ...

In this editorial, I pass on to a new team. South African Computer Journal has moved long way since took over as editor-in-chief 10 years ago and am pleased that we have new, enthusiastic team who will take it heights.
 Katherine Malan is the Etienne van der Poel takes from James Dibley production editor.
 did main work of marshalling papers issue shared final layout checks. All made ...

We analyze a directed variation of the book embedding problem when the page partition is prespecified and the nodes on the spine must be in topological order (upward book embedding). Given a directed acyclic graph and a partition of its edges into k pages, can we linearly order the vertices such that the drawing is upward (a topological sort) and each page avoids crossings? We prove that the pr...

Hyperoperations are mappings that assign a non-void subset of a set to each n-tuple of elements from the set. They present a fundamental notion for modeling non deterministic processes. Even though for each non deterministic automaton there is a language equivalent deterministic automaton, they do not have the same behavior. As behavior of concurrent processes took place in emerging fields of t...

This paper develops a mobility measure that combines desirable features of the relative and absolute approaches to measuring mobility. From the relative approach we borrow the idea that income growth accruing to the relatively poor is more to be valued than income growth to the relatively rich. From the absolute approach we take the idea that upward changes are to be valued, in and of themselve...