set vari IATOM int atom sele pair site 1 end
if ( IATOM .le. 0 ) return
set vari XATOM int atom sele by pair atom numb IATOM end
if ( XATOM .le. 0 ) return
! show vari IATOM
! show vari XATOM
set vari CHR1 char seq sele by resi atom numb IATOM end 
set vari CHR2 char seq sele by resi atom numb XATOM end 

!show vari CHR*

if ( CHR1 .eq. CHR2 ) then
key half_wat sele half_wat .o atom numb IATOM end
else
key out sele out .o by seq atom numb XATOM .a resi name HOH end
end_if
! wr sele out end seq
! wr sele by seq atom numb IATOM .o by seq atom numb XATOM end pair

dele pair sele by seq atom numb IATOM end sele by seq atom numb XATOM end 
dele pair sele by seq atom numb XATOM end sele by seq atom numb IATOM end 
! wr pair
rewind file