Start down the d=4 rabbit hole

Create a Point4 subclass of Point_d so that we can add timeslice info
Which requires using the CGAL 4.5 Epick_d kernel
Which requires using the EIGEN library
Which requires modifying CMakeLists.txt to use it

Which currently gives the following error when you run unittests

dyld: Library not loaded: libCGAL_Core.10.dylib
  Referenced from: /Users/adam/CDT-plusplus/./build/unittests
  Reason: image not found
Trace/BPT trap: 5