fdift.h
#if defined linearized_advection
#else
# if defined fourth_order_tracer_advection || defined quicker
# else
#  if defined fct || defined isoneutralmix
#  else
#  endif
# endif
#endif
#if defined gent_mcwilliams && defined isopycmix
#endif
#if defined consthmix && !defined biharmonic && !defined isopycmix
# if defined bryan_lewis_horizontal
# else
# endif
#else
#endif
#if defined implicitvmix || defined isopycmix || defined isoneutralmix || defined redi_diffusion
#endif
#if defined isopycmix || defined isoneutralmix
#endif