restrict none
define set1 (*:*.O3*, *:*.O4*, *:*.O5*)
define set2 *:*.O?P 
define set3 (dna and not backbone) and nitrogen

select dna
wireframe 20
pause
select set1
cpk 100
pause
cpk off
select set2
cpk 100
pause
cpk off
select set13
cpk 100
pause