message: alpha complex persistence now requires cgal 5.1
diff: project(Alpha_complex_utilities)
  -if (NOT CGAL_WITH_EIGEN3_VERSION VERSION_LESS 4.11.0)
  +if (NOT CGAL_WITH_EIGEN3_VERSION VERSION_LESS 5.1.0)
  add_executable (alpha_complex_persistence alpha_complex_persistence.cpp)
  target_link_libraries(alpha_complex_persistence ${CGAL_LIBRARY} Boost::program_options)
  @@ -27,7 +27,7 @@ if (NOT CGAL_WITH_EIGEN3_VERSION VERSION_LESS 4.11.0)
  endif()
  install(TARGETS alpha_complex_persistence DESTINATION bin)
  -endif (NOT CGAL_WITH_EIGEN3_VERSION VERSION_LESS 4.11.0)
  +endif (NOT CGAL_WITH_EIGEN3_VERSION VERSION_LESS 5.1.0)
  if (NOT CGAL_VERSION VERSION_LESS 4.11.0)
  add_executable(alpha_complex_3d_persistence alpha_complex_3d_persistence.cpp)
  