Figure: 
: Evolution from a joined (gap 0)
pair.
Many evolutionary rules are distinguished by the presence of numerous
inverted triangles in their space-time diagrams. The evolution of pure
cycles shows them to especial advantage, often exhibiting a fractal
structure[117]. Indeed, strings of any arbitrary format can be
expected to show up occasionally; but quiescent strings are of particular
interest because they can only disappear gradually, as live cells
encroach on their boundaries. Triangles are the visual evidence of the
eventual regrowth of the live region, evident in Figure 
.