Hi Ron, Ozone "reaches" high concentrations twelve miles above Earth, where it has long appeared that it was immune from human influence; we have now realized, though, that emissions of industrial chlorofluorocarbons deplete the ozone layer. A) has long appeared that it was immune from B)...

Hi ron am sorry am bumping into an old thread.. but ive always had this fundamental problem of identifying combinatronics problem whether it is an "AND" problem or an "OR" problem.. i understood your session on combinations problems.. but this aspect i was just not able to take.....