Generalizing the two examples given above, answer the following questions using the meet and join operations $($the meet ab is the greatest element below a and b; the join a b is the least element above a and b$)$: Given two objects o$1,$ o$2$ at different security levels s$1$ and s$2$ what is the maximal security level Lmax a subject u can have to be allowed to write both objects? Given two subjects u$1,$ u$2$ at different security levels s$1$ and s$2,$ what is the minimal security level Lmin an object o must have so that both subjects can still write on it$?3$