This code was written by Frank  Lippold / Ralph  Wieland based on
the planarity test by Hopcroft and Tarjan.

HTplanar.c holds the code for the planarity test.
HTembed.c holds a modified planarity test that produces a planar embedding.

'main' procedures are :
HTplanar.c : RESULT planarity (graph)
             Sgraph graph;
HTembed.c :  RESULT embed (graph)
             Sgraph graph;
             graph->attrs.data holds an Slist of edges that is the clockwise
             ordering of edges in the planar embedding.
RESULT is one of
SUCCESS, NONPLANAR, SELF_LOOP, MULTIPLE_EDGE, NO_MEM

HTmain.c contains example calls to planaroty and embed.

All files are (C) University of Passau. Feel free to redistribute
this code. Changes in the code should be marked.
