anchor.diff:  module mod_splitSingletrack
  +
     use iso_fortran_env, only : output_unit
  +
     implicit none
   
     ! File units used for I/O;
  
positive.code:   double precision, private  :: ta(6,6)
  
  contains
    function numSTFpairs(ifname)
      character(len=*), intent(in) :: ifname
      integer numSTFpairs
      integer iostat
  
negative.code:   end function numSTFpairs
  
    subroutine convertSTFpair(pairIdx, ifname, ofname)
  
      integer, intent(in)          :: pairIdx !Which pair to extract
      character(len=*), intent(in) :: ifname  !Name of the singletrackfile to split
      character(len=*), intent(in) :: ofname  !Name of the output file
  
      integer iostat
      integer iPair
      double precision, parameter :: zero = 0.0d0
  
      open(unit=inUnit,  file=ifname, form='UNFORMATTED', status='OLD',     action='READ',  err=410, iostat=iostat)
      open(unit=outUnit, file=ofname, form='UNFORMATTED', status='REPLACE', action='WRITE', err=411, iostat=iostat)
  