anchor.diff:         do i=1,n0
           write(fn_in,*) atag(i),(c(k,i),k=1,3)
          end do
  -       write(*,*) "out "//pname
          return
   c      -------------
   c      error section
  
positive.code:        character*4 a4
         character*255 buf
         logical ofile
         integer fns,fnc,fno      
         integer iat,ires,ires0
         integer nrs
  
negative.code:             if(is_integer(buffer)) then
                read(buffer,*) ida(k)
              else
                message = "two atom ids are required to define the axis"
                goto 911
              end if
             end do
  