Each little quartet of L's represents one function.  The L in the
upper left position specifies the image of an upper-left type L, and
so on.  The functions are themselves arranged in quartets; within each
quartet, only the mapping of the lower right L varies.  These quartets
of functions are further arranged into larger quartets in which the
mapping of the lower left L also varies.  A similar process produces the
next two levels of the hierarchy.  <p>

The figure was produced by a Scheme program, running under Scheme 48,
that generated Postscript code.  Ghostscript interpreted the
postscript to make some kind of bitmap (I forget), which "xv"
converted to a GIF. <p>