For today's mathfitti, let's define m(A) to be the length of the smallest period of a function on some domain, if it exists. So if A is sin(x), m(A) is 2pi, and if A is the characteristic function of the rationals, then we do not define m(A). Suppose A and B are such that m(A) is 3 and m(B) is 6. How small can m(A+B) get? If a=m(A), b=m(B), and c=m(C), when can we get a good estimate of m(A+B+C)?