anchor.diff:        iEl=iu
         ixEl=ix
         bez(ixEl)='e.latt.aper'
  +      bezs(iEl)=bez(ixEl)
         write(lout,"(a)") "APER> -> Inserted empty marker at end of lattice"
       end if
     else if( iEl.eq.1 ) then
  
positive.code: subroutine copy_aperture( ixApeTo, ixApeFrom, nKApe, nApe )
  !-----------------------------------------------------------------------
  !     by A.Mereghetti
  !     last modified: 02-12-2016
  !     copy aperture, either from an existing one or from the one
  !       received on the fly
  !-----------------------------------------------------------------------
    implicit none
  
  ! interface variables
    integer ixApeTo, ixApeFrom, nKApe
    real(kind=fPrec) nApe(11)
  
    if( ixApeFrom.gt.0 ) then
  ! copy aperture marker from existing SINGLE ELEMENT
  
negative.code: subroutine contour_aperture_markers( itElUp, itElDw, lInsUp )
  !-----------------------------------------------------------------------
  ! by A.Mereghetti
  ! last modified: 25-07-2019
  ! check elements itElUp (upstream) and itElDw (downstream) and
  !   assign them (or insert) an aperture marker, in case;
  ! lInsUp: force the insertion of an aperture marker upstream
  