# The "dia" faces at the bottom don't work properly...
# In patricular, the 3 verts indicated here are interpreted as a "tri" face:
#
#         +
#          \-
#          | +  <--
#       +---+ |
#        --  -\
#          +---+
#
#          ^   ^
#          |   |
#


       +---+
       |   |--
       |   |2 +---+
       |1  |--|   |
       +---+3 |   |
     -- | | --|A  |
    +   |4|   +---+
     |   *   |
     |B-- --0|
      +     +   +
            || ||
         +  || ||  +
          \-| + |-/
          | +3|2+ |
       +---+4|||1+---+
        -- 5-\|/-0 --
          +---+---+